D. J. Bernstein
Internet mail

Building a POP toaster

A POP toaster receives mail for authorized users and lets them pick it up through the network.

A POP toaster has three essential components:

  1. Mailbox storage: saving incoming messages on disk.
  2. Mailbox service: letting users pick up mail through the network.
  3. Account management: setting passwords for authorized users.
Some common sendmail-compatible choices:
  1. Mailbox storage: mbox format in /var/spool/mail/$USER.
  2. Mailbox service: qpopper or ipop3d. (Beware that all versions of qpopper before 2.51 allow remote users to take over the machine.)
  3. Account management: UNIX accounts in /etc/passwd.
All of these work with qmail if you continue to deliver mail to /var/spool/mail. See INSTALL.vsm in the qmail package.

qmail offers another choice providing more flexibility:

  1. Mailbox storage: maildir format in $HOME/Maildir.
  2. Mailbox service: qmail-pop3d, part of the qmail package.
  3. Account management: See below.
qmail-pop3d's modular design lets it work with a variety of account-management mechanisms: