documentation_complete: true

title: 'Mail Server Software'

description: |-
    Mail servers are used to send and receive email over the network.
    Mail is a very common service, and Mail Transfer Agents (MTAs) are obvious
    targets of network attack.
    Ensure that systems are not running MTAs unnecessarily,
    and configure needed MTAs as defensively as possible.
    <br /><br />
    Very few systems at any site should be configured to directly receive email over the
    network. Users should instead use mail client programs to retrieve email
    from a central server that supports protocols such as IMAP or POP3.
    However, it is normal for most systems to be independently capable of sending email,
    for instance so that cron jobs can report output to an administrator.
    Most MTAs, including Postfix, support a submission-only mode in which mail can be sent from
    the local system to a central site MTA (or directly delivered to a local account),
    but the system still cannot receive mail directly over a network.
    <br /><br />
    The <tt>alternatives</tt> program in Red Hat Enterprise Linux permits selection of other mail server software
    (such as Sendmail), but Postfix is the default and is preferred.
    Postfix was coded with security in mind and can also be more effectively contained by
    SELinux as its modular design has resulted in separate processes performing specific actions.
    More information is available on its website, <weblink-macro link="http://www.postfix.org" />.
