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Local Delivery Agent
Mail is transferred from incoming mail storage to the mail recipient’s inbox by a local
delivery agent (LDA). The LDA handles local delivery, making mail accessible by the
user’s mail application. Two protocols are available from the Mac OS X Server LDA:
POP and IMAP.
Mac OS X Server uses Dovecot to provide POP and IMAP service. Your mail users will set
their mail application’s incoming mail server to your Mac OS X Server running Dovecot.
More information about Dovecot can be found at: http://www.dovecot.org/.
Dovecot
Dovecot is an open-source enterprise mail system for use in small to large enterprise
environments. Dovecot developers have focused on security, scalability, and ease
of administration.
Each message is stored as a separate le in a mail folder for each user. This design
gives the server advantages in eciency, scalability, and administration. User access to
mail is primarily through software using IMAP or POP3.
Dovecot uses the conguration le /etc/dovecot/dovecot.conf. Server Admin uses
the defaults le /etc/dovecot/dovecot.conf.default. Dovecot logs its events in
/var/log/mailaccess.log. The Dovecot mail store is located in /var/imap/ and user
folders are located in /var/spool/imap/.
The Dovecot delivery application receives mail from the Postx delivery agent and
stores the mail in user spool les in /var/spool/imap/dovecot/mail/GUID, where GUID is
the Globally Unique ID (GUID) of the mail user. The user can then use IMAP or POP to
retrieve messages.
After receiving mail from external MTAs, you can apply virus ltering or junk mail
ltering to the messages. Mac OS X Server uses ClamAV and Spam Assassin for these
tasks. For more information on enabling these, see “Limiting Junk Mail and Viruses”
on page 34.
For more information about Dovecot, see http://www.dovecot.org/.
Internet Message Access Protocol (IMAP)
IMAP is the solution for people who use more than one computer to receive mail.
IMAP is a client-server mail protocol that allows users to access mail from anywhere on
the Internet.
With IMAP, a user’s mail is delivered to the server and stored in a remote mailbox on
the server. To users, mail appears as if it were on the local computer.
A key dierence between IMAP and POP is that with IMAP the mail isn’t removed from
the server until the user deletes it.
16 Chapter 1 Understanding Mail Service