LESSON 10

Date: 4/9/2009
Email Basics
Linux for Engineering and IT applications


Popular Unix SMTP servers

  • Sendmail (http://www.sendmail.org)
    The most widely used. Installable on any Linux distribution as a binary or can compiled from the source. Monolytic implementation. Many applications imply Sendmail availability. Complex configuration file format. Inbox format to store e-mail.

  • Exim (http://www.exim.org)
    Almost the same capabilities as in Sendmail. Simpler configuration than in Sendmail. Monolitic implementation.

  • Postfix (http://www.postfix.org) Simple configuration file format. Easy to setup. Modular implementation. Enchanced security, filtering and performace features. Supports both Inbox and Maildir formats.

  • Qmail (http://www.qmail.org)
    Relatively simple configuration file. Modular design. Maildir format to store e-mail.

    How e-mail is stored (Mail file formats)

  • Inbox (or mbox): e-mail is appended to file /var/mail/$USER
    (default: Sendmail, Exim, Postfix) Advantage: one file per user. Disadvantage: locking when accessed by several processes at the same time, therefore, it should not be shared over NFS.

  • Maildir: a new e-mail is placed in a new file in directory $HOME/Maildir
    (default: Qmail; can be set for Exim and Postfix) Advantages: much rare locking; can be shared over NFS; simply delete e-mail by deleting files. Disadvantage: too many files on busy multi-user systems -- may run out of inodes.

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