Postfix manual - smtp(8)

    SMTP(8)                                                                SMTP(8)

    NAME
           smtp - Postfix SMTP+LMTP client

    SYNOPSIS
           smtp [generic Postfix daemon options] [flags=DORX]

    DESCRIPTION
           The Postfix SMTP+LMTP client implements the SMTP and LMTP mail delivery
           protocols. It processes message delivery requests from the  queue  man-
           ager.  Each  request specifies a queue file, a sender address, a domain
           or host to deliver to, and recipient information.  This program expects
           to be run from the master(8) process manager.

           The  SMTP+LMTP  client  updates  the queue file and marks recipients as
           finished, or it informs the queue manager that delivery should be tried
           again  at  a  later  time.  Delivery  status  reports  are  sent to the
           bounce(8), defer(8) or trace(8) daemon as appropriate.

           The SMTP+LMTP client looks up a list of mail  exchanger  addresses  for
           the  destination  host,  sorts  the list by preference, and connects to
           each listed address until it finds a server that responds.

           When a server is not reachable, or when mail delivery fails  due  to  a
           recoverable  error  condition, the SMTP+LMTP client will try to deliver
           the mail to an alternate host.

           After a successful mail transaction, a connection may be saved  to  the
           scache(8)  connection  cache  server,  so  that  it  may be used by any
           SMTP+LMTP client for a subsequent transaction.

           By default, connection caching is enabled temporarily for  destinations
           that have a high volume of mail in the active queue. Connection caching
           can be enabled permanently for specific destinations.

    SMTP DESTINATION SYNTAX
           The Postfix SMTP+LMTP client supports multiple  destinations  separated
           by comma or whitespace (Postfix 3.5 and later).  SMTP destinations have
           the following form:

           domainname

           domainname:port
                  Look up the mail exchangers for the specified domain,  and  con-
                  nect to the specified port (default: smtp).

           [hostname]

           [hostname]:port
                  Look  up  the  address(es) of the specified host, and connect to
                  the specified port (default: smtp).

           [address]

           [address]:port
                  Connect to the host at the specified address, and connect to the
                  specified  port (default: smtp). An IPv6 address must be format-
                  ted as [ipv6:address].

    LMTP DESTINATION SYNTAX
           The Postfix SMTP+LMTP client supports multiple  destinations  separated
           by comma or whitespace (Postfix 3.5 and later).  LMTP destinations have
           the following form:

           unix:pathname
                  Connect to the local UNIX-domain server that  is  bound  to  the
                  specified  pathname.  If  the process runs chrooted, an absolute
                  pathname is interpreted relative to the Postfix queue directory.

           inet:hostname

           inet:hostname:port

           inet:[address]

           inet:[address]:port
                  Connect  to  the  specified  TCP  port on the specified local or
                  remote host. If no  port  is  specified,  connect  to  the  port
                  defined  as  lmtp  in services(4).  If no such service is found,
                  the lmtp_tcp_port configuration parameter (default value of  24)
                  will   be   used.    An   IPv6  address  must  be  formatted  as
                  [ipv6:address].

    SINGLE-RECIPIENT DELIVERY
           By default, the Postfix SMTP+LMTP  client  delivers  mail  to  multiple
           recipients  per delivery request. This is undesirable when prepending a
           Delivered-to: or X-Original-To: message header. To prevent Postfix from
           sending multiple recipients per delivery request, specify

               transport_destination_recipient_limit = 1

           in  the  Postfix main.cf file, where transport is the name in the first
           column of the Postfix master.cf entry for this mail delivery service.

    COMMAND ATTRIBUTE SYNTAX
           flags=DORX (optional)
                  Optional message processing flags.

                  D      Prepend a "Delivered-To: recipient" message  header  with
                         the  envelope  recipient address. Note: for this to work,
                         the transport_destination_recipient_limit must be 1  (see
                         SINGLE-RECIPIENT DELIVERY above for details).

                         The  D  flag  also  enforces loop detection: if a message
                         already contains a Delivered-To:  header  with  the  same
                         recipient  address, then the message is returned as unde-
                         liverable. The address comparison is case insensitive.

                         This feature is available as of Postfix 3.5.

                  O      Prepend an "X-Original-To: recipient" message header with
                         the recipient address as given to Postfix. Note: for this
                         to work, the  transport_destination_recipient_limit  must
                         be 1 (see SINGLE-RECIPIENT DELIVERY above for details).

                         This feature is available as of Postfix 3.5.

                  R      Prepend a "Return-Path: <sender>" message header with the
                         envelope sender address.

                         This feature is available as of Postfix 3.5.

                  X      Indicates that the delivery is final. This  flag  affects
                         the  status  reported  in  "success" DSN (delivery status
                         notification) messages, and  changes  it  from  "relayed"
                         into "delivered".

                         This feature is available as of Postfix 3.5.

    SECURITY
           The SMTP+LMTP client is moderately security-sensitive. It
           talks to SMTP or LMTP servers and to DNS servers on the
           network. The SMTP+LMTP client can be run chrooted at fixed
           low privilege.

    STANDARDS
           RFC 821 (SMTP protocol)
           RFC 822 (ARPA Internet Text Messages)
           RFC 1651 (SMTP service extensions)
           RFC 1652 (8bit-MIME transport)
           RFC 1870 (Message Size Declaration)
           RFC 2033 (LMTP protocol)
           RFC 2034 (SMTP Enhanced Error Codes)
           RFC 2045 (MIME: Format of Internet Message Bodies)
           RFC 2046 (MIME: Media Types)
           RFC 2554 (AUTH command)
           RFC 2821 (SMTP protocol)
           RFC 2920 (SMTP Pipelining)
           RFC 3207 (STARTTLS command)
           RFC 3461 (SMTP DSN Extension)
           RFC 3463 (Enhanced Status Codes)
           RFC 4954 (AUTH command)
           RFC 5321 (SMTP protocol)
           RFC 6531 (Internationalized SMTP)
           RFC 6533 (Internationalized Delivery Status Notifications)
           RFC 7672 (SMTP security via opportunistic DANE TLS)

    DIAGNOSTICS
           Problems  and  transactions  are  logged  to syslogd(8) or postlogd(8).
           Corrupted message files are marked so that the queue manager  can  move
           them to the corrupt queue for further inspection.

           Depending  on the setting of the notify_classes parameter, the postmas-
           ter is notified of bounces, protocol problems, and of other trouble.

    BUGS
           SMTP and LMTP connection reuse for TLS (without  closing  the  SMTP  or
           LMTP connection) is not supported before Postfix 3.4.

           SMTP  and LMTP connection reuse assumes that SASL credentials are valid
           for all destinations that map onto the same IP address and TCP port.

    CONFIGURATION PARAMETERS
           Before Postfix version 2.3, the LMTP client is a separate program  that
           implements  only  a  subset  of  the functionality available with SMTP:
           there is no support for TLS, and  connections  are  cached  in-process,
           making it ineffective when the client is used for multiple domains.

           Most smtp_xxx configuration parameters have an lmtp_xxx "mirror" param-
           eter for the equivalent LMTP  feature.  This  document  describes  only
           those LMTP-related parameters that aren't simply "mirror" parameters.

           Changes  to  main.cf  are picked up automatically, as smtp(8) processes
           run for only a limited amount of time. Use the command "postfix reload"
           to speed up a change.

           The  text  below provides only a parameter summary. See postconf(5) for
           more details including examples.

    COMPATIBILITY CONTROLS
           ignore_mx_lookup_error (no)
                  Ignore DNS MX lookups that produce no response.

           smtp_always_send_ehlo (yes)
                  Always send EHLO at the start of an SMTP session.

           smtp_never_send_ehlo (no)
                  Never send EHLO at the start of an SMTP session.

           smtp_defer_if_no_mx_address_found (no)
                  Defer mail delivery when no MX record resolves to an IP address.

           smtp_line_length_limit (998)
                  The maximal length of message header and body lines that Postfix
                  will send via SMTP.

           smtp_pix_workaround_delay_time (10s)
                  How  long  the  Postfix  SMTP  client  pauses   before   sending
                  ".<CR><LF>"   in   order   to   work  around  the  PIX  firewall
                  "<CR><LF>.<CR><LF>" bug.

           smtp_pix_workaround_threshold_time (500s)
                  How long a message must be queued before the Postfix SMTP client
                  turns on the PIX firewall "<CR><LF>.<CR><LF>" bug workaround for
                  delivery through firewalls with "smtp fixup" mode turned on.

           smtp_pix_workarounds (disable_esmtp, delay_dotcrlf)
                  A list that specifies zero or more  workarounds  for  CISCO  PIX
                  firewall bugs.

           smtp_pix_workaround_maps (empty)
                  Lookup  tables,  indexed by the remote SMTP server address, with
                  per-destination workarounds for CISCO PIX firewall bugs.

           smtp_quote_rfc821_envelope (yes)
                  Quote addresses in Postfix SMTP client MAIL  FROM  and  RCPT  TO
                  commands as required by RFC 5321.

           smtp_reply_filter (empty)
                  A  mechanism  to  transform replies from remote SMTP servers one
                  line at a time.

           smtp_skip_5xx_greeting (yes)
                  Skip remote SMTP servers that greet with a 5XX status code.

           smtp_skip_quit_response (yes)
                  Do not wait for the response to the SMTP QUIT command.

           Available in Postfix version 2.0 and earlier:

           smtp_skip_4xx_greeting (yes)
                  Skip SMTP servers that greet with a 4XX status  code  (go  away,
                  try again later).

           Available in Postfix version 2.2 and later:

           smtp_discard_ehlo_keyword_address_maps (empty)
                  Lookup  tables,  indexed by the remote SMTP server address, with
                  case insensitive lists of EHLO keywords  (pipelining,  starttls,
                  auth, etc.) that the Postfix SMTP client will ignore in the EHLO
                  response from a remote SMTP server.

           smtp_discard_ehlo_keywords (empty)
                  A case insensitive list of EHLO keywords (pipelining,  starttls,
                  auth, etc.) that the Postfix SMTP client will ignore in the EHLO
                  response from a remote SMTP server.

           smtp_generic_maps (empty)
                  Optional lookup tables that perform  address  rewriting  in  the
                  Postfix  SMTP  client,  typically  to  transform a locally valid
                  address into a globally valid address when sending  mail  across
                  the Internet.

           Available in Postfix version 2.2.9 and later:

           smtp_cname_overrides_servername (version dependent)
                  When  the  remote  SMTP  servername  is a DNS CNAME, replace the
                  servername with the result from CNAME expansion for the  purpose
                  of  logging,  SASL password lookup, TLS policy decisions, or TLS
                  certificate verification.

           Available in Postfix version 2.3 and later:

           lmtp_discard_lhlo_keyword_address_maps (empty)
                  Lookup tables, indexed by the remote LMTP server  address,  with
                  case  insensitive  lists of LHLO keywords (pipelining, starttls,
                  auth, etc.) that the Postfix LMTP client will ignore in the LHLO
                  response from a remote LMTP server.

           lmtp_discard_lhlo_keywords (empty)
                  A  case insensitive list of LHLO keywords (pipelining, starttls,
                  auth, etc.) that the Postfix LMTP client will ignore in the LHLO
                  response from a remote LMTP server.

           Available in Postfix version 2.4.4 and later:

           send_cyrus_sasl_authzid (no)
                  When  authenticating  to  a  remote SMTP or LMTP server with the
                  default setting "no", send no SASL authoriZation  ID  (authzid);
                  send  only  the  SASL authentiCation ID (authcid) plus the auth-
                  cid's password.

           Available in Postfix version 2.5 and later:

           smtp_header_checks (empty)
                  Restricted header_checks(5) tables for the Postfix SMTP  client.

           smtp_mime_header_checks (empty)
                  Restricted  mime_header_checks(5)  tables  for  the Postfix SMTP
                  client.

           smtp_nested_header_checks (empty)
                  Restricted nested_header_checks(5) tables for the  Postfix  SMTP
                  client.

           smtp_body_checks (empty)
                  Restricted body_checks(5) tables for the Postfix SMTP client.

           Available in Postfix version 2.6 and later:

           tcp_windowsize (0)
                  An  optional  workaround for routers that break TCP window scal-
                  ing.

           Available in Postfix version 2.8 and later:

           smtp_dns_resolver_options (empty)
                  DNS Resolver options for the Postfix SMTP client.

           Available in Postfix version 2.9 and later:

           smtp_per_record_deadline (no)
                  Change the behavior of the smtp_*_timeout time  limits,  from  a
                  time  limit  per  read  or write system call, to a time limit to
                  send or receive a complete record (an SMTP  command  line,  SMTP
                  response  line,  SMTP message content line, or TLS protocol mes-
                  sage).

           smtp_send_dummy_mail_auth (no)
                  Whether or not to append the "AUTH=<>" option to the  MAIL  FROM
                  command in SASL-authenticated SMTP sessions.

           Available in Postfix version 2.11 and later:

           smtp_dns_support_level (empty)
                  Level of DNS support in the Postfix SMTP client.

           Available in Postfix version 3.0 and later:

           smtp_delivery_status_filter ($default_delivery_status_filter)
                  Optional  filter  for  the  smtp(8) delivery agent to change the
                  delivery status code or explanatory text of successful or unsuc-
                  cessful deliveries.

           smtp_dns_reply_filter (empty)
                  Optional filter for Postfix SMTP client DNS lookup results.

           Available in Postfix version 3.3 and later:

           smtp_balance_inet_protocols (yes)
                  When  a remote destination resolves to a combination of IPv4 and
                  IPv6 addresses, ensure that the Postfix SMTP client can try both
                  address types before it runs into the smtp_mx_address_limit.

           Available in Postfix 3.5 and later:

           info_log_address_format (external)
                  The  email  address  form that will be used in non-debug logging
                  (info, warning, etc.).

           Available in Postfix 3.5.9 and later:

           dnssec_probe (ns:.)
                  The DNS query type (default: "ns") and DNS query name  (default:
                  ".") that Postfix may use to determine whether DNSSEC validation
                  is available.

    MIME PROCESSING CONTROLS
           Available in Postfix version 2.0 and later:

           disable_mime_output_conversion (no)
                  Disable the conversion of 8BITMIME format to 7BIT format.

           mime_boundary_length_limit (2048)
                  The maximal length of MIME multipart boundary strings.

           mime_nesting_limit (100)
                  The maximal recursion level that the MIME processor will handle.

    EXTERNAL CONTENT INSPECTION CONTROLS
           Available in Postfix version 2.1 and later:

           smtp_send_xforward_command (no)
                  Send  the  non-standard  XFORWARD  command when the Postfix SMTP
                  server EHLO response announces XFORWARD support.

    SASL AUTHENTICATION CONTROLS
           smtp_sasl_auth_enable (no)
                  Enable SASL authentication in the Postfix SMTP client.

           smtp_sasl_password_maps (empty)
                  Optional Postfix  SMTP  client  lookup  tables  with  one  user-
                  name:password  entry  per  sender,  remote  hostname or next-hop
                  domain.

           smtp_sasl_security_options (noplaintext, noanonymous)
                  Postfix SMTP client SASL security options; as of Postfix 2.3 the
                  list  of available features depends on the SASL client implemen-
                  tation that is selected with smtp_sasl_type.

           Available in Postfix version 2.2 and later:

           smtp_sasl_mechanism_filter (empty)
                  If non-empty, a Postfix SMTP client filter for the  remote  SMTP
                  server's list of offered SASL mechanisms.

           Available in Postfix version 2.3 and later:

           smtp_sender_dependent_authentication (no)
                  Enable  sender-dependent  authentication  in  the  Postfix  SMTP
                  client; this is available only  with  SASL  authentication,  and
                  disables  SMTP  connection caching to ensure that mail from dif-
                  ferent senders will use the appropriate credentials.

           smtp_sasl_path (empty)
                  Implementation-specific information that the Postfix SMTP client
                  passes  through  to  the  SASL  plug-in  implementation  that is
                  selected with smtp_sasl_type.

           smtp_sasl_type (cyrus)
                  The SASL plug-in type that the Postfix SMTP  client  should  use
                  for authentication.

           Available in Postfix version 2.5 and later:

           smtp_sasl_auth_cache_name (empty)
                  An  optional table to prevent repeated SASL authentication fail-
                  ures with the same remote SMTP  server  hostname,  username  and
                  password.

           smtp_sasl_auth_cache_time (90d)
                  The  maximal age of an smtp_sasl_auth_cache_name entry before it
                  is removed.

           smtp_sasl_auth_soft_bounce (yes)
                  When a remote SMTP server rejects a SASL authentication  request
                  with  a 535 reply code, defer mail delivery instead of returning
                  mail as undeliverable.

           Available in Postfix version 2.9 and later:

           smtp_send_dummy_mail_auth (no)
                  Whether or not to append the "AUTH=<>" option to the  MAIL  FROM
                  command in SASL-authenticated SMTP sessions.

    STARTTLS SUPPORT CONTROLS
           Detailed  information  about STARTTLS configuration may be found in the
           TLS_README document.

           smtp_tls_security_level (empty)
                  The default SMTP TLS security level for the Postfix SMTP client;
                  when a non-empty value is specified, this overrides the obsolete
                  parameters       smtp_use_tls,       smtp_enforce_tls,       and
                  smtp_tls_enforce_peername.

           smtp_sasl_tls_security_options ($smtp_sasl_security_options)
                  The  SASL  authentication security options that the Postfix SMTP
                  client uses for TLS encrypted SMTP sessions.

           smtp_starttls_timeout (300s)
                  Time limit for Postfix SMTP client  write  and  read  operations
                  during TLS startup and shutdown handshake procedures.

           smtp_tls_CAfile (empty)
                  A  file  containing  CA certificates of root CAs trusted to sign
                  either remote SMTP server certificates or intermediate  CA  cer-
                  tificates.

           smtp_tls_CApath (empty)
                  Directory  with  PEM format Certification Authority certificates
                  that the Postfix SMTP client uses to verify a remote SMTP server
                  certificate.

           smtp_tls_cert_file (empty)
                  File with the Postfix SMTP client RSA certificate in PEM format.

           smtp_tls_mandatory_ciphers (medium)
                  The minimum TLS cipher grade that the Postfix SMTP  client  will
                  use with mandatory TLS encryption.

           smtp_tls_exclude_ciphers (empty)
                  List of ciphers or cipher types to exclude from the Postfix SMTP
                  client cipher list at all TLS security levels.

           smtp_tls_mandatory_exclude_ciphers (empty)
                  Additional list of ciphers or cipher types to exclude  from  the
                  Postfix  SMTP  client cipher list at mandatory TLS security lev-
                  els.

           smtp_tls_dcert_file (empty)
                  File with the Postfix SMTP client DSA certificate in PEM format.

           smtp_tls_dkey_file ($smtp_tls_dcert_file)
                  File with the Postfix SMTP client DSA private key in PEM format.

           smtp_tls_key_file ($smtp_tls_cert_file)
                  File with the Postfix SMTP client RSA private key in PEM format.

           smtp_tls_loglevel (0)
                  Enable additional Postfix SMTP client logging of TLS activity.

           smtp_tls_note_starttls_offer (no)
                  Log  the  hostname of a remote SMTP server that offers STARTTLS,
                  when TLS is not already enabled for that server.

           smtp_tls_policy_maps (empty)
                  Optional lookup tables with the Postfix SMTP client TLS security
                  policy by next-hop destination; when a non-empty value is speci-
                  fied, this overrides the obsolete smtp_tls_per_site parameter.

           smtp_tls_mandatory_protocols (!SSLv2, !SSLv3)
                  List of SSL/TLS protocols that the Postfix SMTP client will  use
                  with mandatory TLS encryption.

           smtp_tls_scert_verifydepth (9)
                  The verification depth for remote SMTP server certificates.

           smtp_tls_secure_cert_match (nexthop, dot-nexthop)
                  How  the  Postfix  SMTP  client  verifies the server certificate
                  peername for the "secure" TLS security level.

           smtp_tls_session_cache_database (empty)
                  Name of the file containing the optional Postfix SMTP client TLS
                  session cache.

           smtp_tls_session_cache_timeout (3600s)
                  The  expiration  time  of  Postfix SMTP client TLS session cache
                  information.

           smtp_tls_verify_cert_match (hostname)
                  How the Postfix SMTP  client  verifies  the  server  certificate
                  peername for the "verify" TLS security level.

           tls_daemon_random_bytes (32)
                  The  number  of  pseudo-random bytes that an smtp(8) or smtpd(8)
                  process requests from the tlsmgr(8) server in order to seed  its
                  internal pseudo random number generator (PRNG).

           tls_high_cipherlist (see 'postconf -d' output)
                  The OpenSSL cipherlist for "high" grade ciphers.

           tls_medium_cipherlist (see 'postconf -d' output)
                  The OpenSSL cipherlist for "medium" or higher grade ciphers.

           tls_low_cipherlist (see 'postconf -d' output)
                  The OpenSSL cipherlist for "low" or higher grade ciphers.

           tls_export_cipherlist (see 'postconf -d' output)
                  The OpenSSL cipherlist for "export" or higher grade ciphers.

           tls_null_cipherlist (eNULL:!aNULL)
                  The  OpenSSL  cipherlist  for  "NULL" grade ciphers that provide
                  authentication without encryption.

           Available in Postfix version 2.4 and later:

           smtp_sasl_tls_verified_security_options           ($smtp_sasl_tls_secu-
           rity_options)
                  The SASL authentication security options that the  Postfix  SMTP
                  client  uses  for  TLS  encrypted  SMTP sessions with a verified
                  server certificate.

           Available in Postfix version 2.5 and later:

           smtp_tls_fingerprint_cert_match (empty)
                  List of acceptable remote SMTP server  certificate  fingerprints
                  for   the   "fingerprint"  TLS  security  level  (smtp_tls_secu-
                  rity_level = fingerprint).

           smtp_tls_fingerprint_digest (md5)
                  The message digest  algorithm  used  to  construct  remote  SMTP
                  server certificate fingerprints.

           Available in Postfix version 2.6 and later:

           smtp_tls_protocols (!SSLv2, !SSLv3)
                  List  of TLS protocols that the Postfix SMTP client will exclude
                  or include with opportunistic TLS encryption.

           smtp_tls_ciphers (medium)
                  The minimum TLS cipher grade that the Postfix SMTP  client  will
                  use with opportunistic TLS encryption.

           smtp_tls_eccert_file (empty)
                  File  with the Postfix SMTP client ECDSA certificate in PEM for-
                  mat.

           smtp_tls_eckey_file ($smtp_tls_eccert_file)
                  File with the Postfix SMTP client ECDSA private key in PEM  for-
                  mat.

           Available in Postfix version 2.7 and later:

           smtp_tls_block_early_mail_reply (no)
                  Try  to  detect  a mail hijacking attack based on a TLS protocol
                  vulnerability (CVE-2009-3555), where an attacker prepends  mali-
                  cious  HELO,  MAIL, RCPT, DATA commands to a Postfix SMTP client
                  TLS session.

           Available in Postfix version 2.8 and later:

           tls_disable_workarounds (see 'postconf -d' output)
                  List or bit-mask of OpenSSL bug work-arounds to disable.

           Available in Postfix version 2.11-3.1:

           tls_dane_digest_agility (on)
                  Configure RFC7671 DANE TLSA digest algorithm agility.

           tls_dane_trust_anchor_digest_enable (yes)
                  Enable support for RFC 6698 (DANE TLSA) DNS records that contain
                  digests of trust-anchors with certificate usage "2".

           Available in Postfix version 2.11 and later:

           smtp_tls_trust_anchor_file (empty)
                  Zero  or  more  PEM-format  files with trust-anchor certificates
                  and/or public keys.

           smtp_tls_force_insecure_host_tlsa_lookup (no)
                  Lookup the associated DANE TLSA RRset even when  a  hostname  is
                  not an alias and its address records lie in an unsigned zone.

           tlsmgr_service_name (tlsmgr)
                  The name of the tlsmgr(8) service entry in master.cf.

           Available in Postfix version 3.0 and later:

           smtp_tls_wrappermode (no)
                  Request  that  the Postfix SMTP client connects using the legacy
                  SMTPS protocol instead of using the STARTTLS command.

           Available in Postfix version 3.1 and later:

           smtp_tls_dane_insecure_mx_policy (dane)
                  The TLS policy for MX hosts with "secure" TLSA records when  the
                  nexthop  destination  security  level is dane, but the MX record
                  was found via an "insecure" MX lookup.

           Available in Postfix version 3.4 and later:

           smtp_tls_connection_reuse (no)
                  Try to make multiple deliveries per TLS-encrypted connection.

           smtp_tls_chain_files (empty)
                  List of one or more PEM files, each holding one or more  private
                  keys directly followed by a corresponding certificate chain.

           smtp_tls_servername (empty)
                  Optional  name  to  send  to  the  remote SMTP server in the TLS
                  Server Name Indication (SNI) extension.

           Available in Postfix 3.5, 3.4.6, 3.3.5, 3.2.10, 3.1.13 and later:

           tls_fast_shutdown_enable (yes)
                  A workaround for implementations that hang Postfix  while  shut-
                  ting down a TLS session, until Postfix times out.

    OBSOLETE STARTTLS CONTROLS
           The  following  configuration  parameters  exist for compatibility with
           Postfix versions before 2.3. Support for these will  be  removed  in  a
           future release.

           smtp_use_tls (no)
                  Opportunistic  mode: use TLS when a remote SMTP server announces
                  STARTTLS support, otherwise send the mail in the clear.

           smtp_enforce_tls (no)
                  Enforcement mode: require  that  remote  SMTP  servers  use  TLS
                  encryption, and never send mail in the clear.

           smtp_tls_enforce_peername (yes)
                  With  mandatory  TLS  encryption,  require  that the remote SMTP
                  server hostname matches  the  information  in  the  remote  SMTP
                  server certificate.

           smtp_tls_per_site (empty)
                  Optional  lookup  tables  with the Postfix SMTP client TLS usage
                  policy by next-hop destination and by remote SMTP  server  host-
                  name.

           smtp_tls_cipherlist (empty)
                  Obsolete  Postfix  < 2.3 control for the Postfix SMTP client TLS
                  cipher list.

    RESOURCE AND RATE CONTROLS
           smtp_connect_timeout (30s)
                  The Postfix SMTP client time limit for completing a TCP  connec-
                  tion, or zero (use the operating system built-in time limit).

           smtp_helo_timeout (300s)
                  The  Postfix SMTP client time limit for sending the HELO or EHLO
                  command, and  for  receiving  the  initial  remote  SMTP  server
                  response.

           lmtp_lhlo_timeout (300s)
                  The Postfix LMTP client time limit for sending the LHLO command,
                  and for receiving the initial remote LMTP server response.

           smtp_xforward_timeout (300s)
                  The Postfix SMTP client time limit for sending the XFORWARD com-
                  mand, and for receiving the remote SMTP server response.

           smtp_mail_timeout (300s)
                  The  Postfix  SMTP  client  time limit for sending the MAIL FROM
                  command, and for receiving the remote SMTP server response.

           smtp_rcpt_timeout (300s)
                  The Postfix SMTP client time limit for sending the SMTP RCPT  TO
                  command, and for receiving the remote SMTP server response.

           smtp_data_init_timeout (120s)
                  The  Postfix  SMTP  client  time limit for sending the SMTP DATA
                  command, and for receiving the remote SMTP server response.

           smtp_data_xfer_timeout (180s)
                  The Postfix SMTP client time limit for sending the SMTP  message
                  content.

           smtp_data_done_timeout (600s)
                  The Postfix SMTP client time limit for sending the SMTP ".", and
                  for receiving the remote SMTP server response.

           smtp_quit_timeout (300s)
                  The Postfix SMTP client time limit for sending the QUIT command,
                  and for receiving the remote SMTP server response.

           Available in Postfix version 2.1 and later:

           smtp_mx_address_limit (5)
                  The  maximal number of MX (mail exchanger) IP addresses that can
                  result from Postfix SMTP client mail exchanger lookups, or  zero
                  (no limit).

           smtp_mx_session_limit (2)
                  The  maximal number of SMTP sessions per delivery request before
                  the Postfix SMTP client gives up  or  delivers  to  a  fall-back
                  relay host, or zero (no limit).

           smtp_rset_timeout (20s)
                  The Postfix SMTP client time limit for sending the RSET command,
                  and for receiving the remote SMTP server response.

           Available in Postfix version 2.2 and earlier:

           lmtp_cache_connection (yes)
                  Keep Postfix LMTP client connections open for  up  to  $max_idle
                  seconds.

           Available in Postfix version 2.2 and later:

           smtp_connection_cache_destinations (empty)
                  Permanently  enable  SMTP  connection  caching for the specified
                  destinations.

           smtp_connection_cache_on_demand (yes)
                  Temporarily enable SMTP connection caching while  a  destination
                  has a high volume of mail in the active queue.

           smtp_connection_reuse_time_limit (300s)
                  The amount of time during which Postfix will use an SMTP connec-
                  tion repeatedly.

           smtp_connection_cache_time_limit (2s)
                  When SMTP connection caching is enabled, the amount of time that
                  an unused SMTP client socket is kept open before it is closed.

           Available in Postfix version 2.3 and later:

           connection_cache_protocol_timeout (5s)
                  Time  limit for connection cache connect, send or receive opera-
                  tions.

           Available in Postfix version 2.9 and later:

           smtp_per_record_deadline (no)
                  Change the behavior of the smtp_*_timeout time  limits,  from  a
                  time  limit  per  read  or write system call, to a time limit to
                  send or receive a complete record (an SMTP  command  line,  SMTP
                  response  line,  SMTP message content line, or TLS protocol mes-
                  sage).

           Available in Postfix version 2.11 and later:

           smtp_connection_reuse_count_limit (0)
                  When SMTP connection caching is enabled,  the  number  of  times
                  that  an SMTP session may be reused before it is closed, or zero
                  (no limit).

           Available in Postfix version 3.4 and later:

           smtp_tls_connection_reuse (no)
                  Try to make multiple deliveries per TLS-encrypted connection.

           Implemented in the qmgr(8) daemon:

           transport_destination_concurrency_limit   ($default_destination_concur-
           rency_limit)
                  A transport-specific override for  the  default_destination_con-
                  currency_limit parameter value, where transport is the master.cf
                  name of the message delivery transport.

           transport_destination_recipient_limit     ($default_destination_recipi-
           ent_limit)
                  A transport-specific override for the default_destination_recip-
                  ient_limit  parameter  value,  where  transport is the master.cf
                  name of the message delivery transport.

    SMTPUTF8 CONTROLS
           Preliminary SMTPUTF8 support is introduced with Postfix 3.0.

           smtputf8_enable (yes)
                  Enable preliminary SMTPUTF8 support for the protocols  described
                  in RFC 6531..6533.

           smtputf8_autodetect_classes (sendmail, verify)
                  Detect  that  a message requires SMTPUTF8 support for the speci-
                  fied mail origin classes.

           Available in Postfix version 3.2 and later:

           enable_idna2003_compatibility (no)
                  Enable  'transitional'  compatibility   between   IDNA2003   and
                  IDNA2008,  when  converting UTF-8 domain names to/from the ASCII
                  form that is used for DNS lookups.

    TROUBLE SHOOTING CONTROLS
           debug_peer_level (2)
                  The increment in verbose logging level when a remote  client  or
                  server matches a pattern in the debug_peer_list parameter.

           debug_peer_list (empty)
                  Optional  list  of  remote  client or server hostname or network
                  address  patterns  that  cause  the  verbose  logging  level  to
                  increase by the amount specified in $debug_peer_level.

           error_notice_recipient (postmaster)
                  The  recipient  of  postmaster notifications about mail delivery
                  problems that are caused by policy, resource, software or proto-
                  col errors.

           internal_mail_filter_classes (empty)
                  What   categories  of  Postfix-generated  mail  are  subject  to
                  before-queue   content    inspection    by    non_smtpd_milters,
                  header_checks and body_checks.

           notify_classes (resource, software)
                  The list of error classes that are reported to the postmaster.

    MISCELLANEOUS CONTROLS
           best_mx_transport (empty)
                  Where  the  Postfix  SMTP  client  should  deliver  mail when it
                  detects a "mail loops back to myself" error condition.

           config_directory (see 'postconf -d' output)
                  The default location of the Postfix main.cf and  master.cf  con-
                  figuration files.

           daemon_timeout (18000s)
                  How  much  time  a  Postfix  daemon process may take to handle a
                  request before it is terminated by a built-in watchdog timer.

           delay_logging_resolution_limit (2)
                  The maximal number of digits after the decimal point  when  log-
                  ging sub-second delay values.

           disable_dns_lookups (no)
                  Disable DNS lookups in the Postfix SMTP and LMTP clients.

           inet_interfaces (all)
                  The  network  interface addresses that this mail system receives
                  mail on.

           inet_protocols (all)
                  The Internet protocols Postfix will attempt to use  when  making
                  or accepting connections.

           ipc_timeout (3600s)
                  The  time  limit  for  sending  or receiving information over an
                  internal communication channel.

           lmtp_assume_final (no)
                  When a remote LMTP server announces no DSN support, assume  that
                  the  server performs final delivery, and send "delivered" deliv-
                  ery status notifications instead of "relayed".

           lmtp_tcp_port (24)
                  The default TCP port that the Postfix LMTP client connects to.

           max_idle (100s)
                  The maximum amount of time that an idle Postfix  daemon  process
                  waits for an incoming connection before terminating voluntarily.

           max_use (100)
                  The maximal number of incoming connections that a Postfix daemon
                  process will service before terminating voluntarily.

           process_id (read-only)
                  The process ID of a Postfix command or daemon process.

           process_name (read-only)
                  The process name of a Postfix command or daemon process.

           proxy_interfaces (empty)
                  The  network  interface addresses that this mail system receives
                  mail on by way of a proxy or network address translation unit.

           smtp_address_preference (any)
                  The address type ("ipv6", "ipv4" or "any") that the Postfix SMTP
                  client  will  try  first,  when  a destination has IPv6 and IPv4
                  addresses with equal MX preference.

           smtp_bind_address (empty)
                  An optional numerical network  address  that  the  Postfix  SMTP
                  client should bind to when making an IPv4 connection.

           smtp_bind_address6 (empty)
                  An  optional  numerical  network  address  that the Postfix SMTP
                  client should bind to when making an IPv6 connection.

           smtp_helo_name ($myhostname)
                  The hostname to send in the SMTP HELO or EHLO command.

           lmtp_lhlo_name ($myhostname)
                  The hostname to send in the LMTP LHLO command.

           smtp_host_lookup (dns)
                  What mechanisms the Postfix SMTP client uses to look up a host's
                  IP address.

           smtp_randomize_addresses (yes)
                  Randomize the order of equal-preference MX host addresses.

           syslog_facility (mail)
                  The syslog facility of Postfix logging.

           syslog_name (see 'postconf -d' output)
                  A  prefix  that  is  prepended  to  the  process  name in syslog
                  records, so that, for example, "smtpd" becomes "prefix/smtpd".

           Available with Postfix 2.2 and earlier:

           fallback_relay (empty)
                  Optional list of relay hosts for SMTP destinations that can't be
                  found or that are unreachable.

           Available with Postfix 2.3 and later:

           smtp_fallback_relay ($fallback_relay)
                  Optional list of relay hosts for SMTP destinations that can't be
                  found or that are unreachable.

           Available with Postfix 3.0 and later:

           smtp_address_verify_target (rcpt)
                  In the context of email address verification, the SMTP  protocol
                  stage that determines whether an email address is deliverable.

           Available with Postfix 3.1 and later:

           lmtp_fallback_relay (empty)
                  Optional list of relay hosts for LMTP destinations that can't be
                  found or that are unreachable.

           Available with Postfix 3.2 and later:

           smtp_tcp_port (smtp)
                  The default TCP port that the Postfix SMTP client connects to.

           Available in Postfix 3.3 and later:

           service_name (read-only)
                  The master.cf service name of a Postfix daemon process.

    SEE ALSO
           generic(5), output address rewriting
           header_checks(5), message header content inspection
           body_checks(5), body parts content inspection
           qmgr(8), queue manager
           bounce(8), delivery status reports
           scache(8), connection cache server
           postconf(5), configuration parameters
           master(5), generic daemon options
           master(8), process manager
           tlsmgr(8), TLS session and PRNG management
           postlogd(8), Postfix logging
           syslogd(8), system logging

    README FILES
           SASL_README, Postfix SASL howto
           TLS_README, Postfix STARTTLS howto

    LICENSE
           The Secure Mailer license must be distributed with this software.

    AUTHOR(S)
           Wietse Venema
           IBM T.J. Watson Research
           P.O. Box 704
           Yorktown Heights, NY 10598, USA

           Wietse Venema
           Google, Inc.
           111 8th Avenue
           New York, NY 10011, USA

           Command pipelining in cooperation with:
           Jon Ribbens
           Oaktree Internet Solutions Ltd.,
           Internet House,
           Canal Basin,
           Coventry,
           CV1 4LY, United Kingdom.

           SASL support originally by:
           Till Franke
           SuSE Rhein/Main AG
           65760 Eschborn, Germany

           TLS support originally by:
           Lutz Jaenicke
           BTU Cottbus
           Allgemeine Elektrotechnik
           Universitaetsplatz 3-4
           D-03044 Cottbus, Germany

           Revised TLS and SMTP connection cache support by:
           Victor Duchovni
           Morgan Stanley

                                                                           SMTP(8)