Linux System Administration

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Chapter 5: Mail

File locking is a mechanism that enforces access to a computer file by

only one user or process at any specific time. The purpose of locking is

to prevent conflicting updates.

Many people consider file locking a problem in the case of mail. Many distributed

filesystems lack reliable locking mechanisms. Some people also believe file locking is

insufficient to prevent occasional mbox corruption. With Linux, corruption is possi-

ble if a mail process is terminated in the middle of updating an mbox.

The maildir format, in contrast, allows concurrent access by multiple applications

and does not require file locking.

Other IMAP servers, such as Cyrus, Courier, and Dovecot, use the maildir format

and allow virtual users and user accounts without shell access and home directories

to access mail. Configured in conjunction with Postfix, the user accounts have only

mailboxes. This allows the administrator to maintain the MTA and MDA without

having to manage standard user accounts on the server itself.

IMAP servers other than uw-imapd are difficult and require significant knowledge to

configure, so you will have to judge for yourself whether the size of your organiza-

tion warrants their use. If so, you’ll need to look at other sources of information,

such as The Book of Postfix by Ralf Hildebrandt and Patrick Katter (No Starch Press).

Email Client Configuration

In our introduction to the ...