testmxlookup

## Name

testmxlookup — Look up mail relays for a domain

## Synopsis

`testmxlookup` [@`ip-address`] [--dnssec] [--udpsize `n`] {`domain`}

## DESCRIPTION

testmxlookup lists the names and IP addresses of mail relays that receive mail for the `domain`. This is useful in diagnosing mail delivery problems.

testmxlookup sends a DNS MX query for the specified domain, followed by A/AAAA queries, if needed. testmxlookup lists the hostname and the IP address of every mail relay, and its MX priority.

### DIAGNOSTICS

The error message "Hard error" indicates that the domain does not exist, or does not have any mail relays. The error message "Soft error" indicates a temporary error condition (usually a network failure of some sorts, or the local DNS server is down).

### OPTIONS

`@ip-address`

  Specify the DNS server's IP address, where to send the DNS query to, overriding the default DNS server addresses read from `/etc/resolv.conf`.

  “ip-address” must be a literal, numeric, IP address.

`--dnssec`

  Enable the `DNSSEC` extension. If the DNS server has `DNSSEC` enabled, and the specified domain's DNS records are signed, the list of IP addresses is suffixed by “(DNSSEC)”, indicating a signed response.

  This is a diagnostic option. Older DNS servers may respond with an error, to a DNSSEC query.

`--udpsize` `n`

  Specify that `n` is the largest UDP packet size that the DNS server may send. This option is only valid together with “--dnssec”. If “--dnssec” always returns an error, try “--udpsize 512” (the default setting is 1280 bytes, which is adequate for Ethernet, but other kinds of networks may impose lower limits).

## SEE ALSO

courier(8), RFC 1035.