Dovecot is a mail delivery agent and IMAP/POP3 server for the email system. Configuration is found in
Local Delivery Agent
The last step in delivering mail to user mailboxes for Exim is to call the dovecot-lda from the exim dovecot_delivery transport. This prompts Dovecot to accept the incoming mail, index it and run the user's Sieve scripts to deliver the email correctly.
Sieve is a mail filtering language used by Dovecot. Simple scripts can be written in .dovecot.sieve in a user's home directory which will act on incoming email for sorting. This is complemented by a tool called ManageSieve which provides a TCP interface to these scripts. This in turn ties in to a RoundCube plugin for mail filtering graphically using webmail (noting that mail filtering is applied whether email is received through IMAP or Webmail). It is also possible to use a ManageSieve plugin for another email client, such as Thunderbird, however to do so at present you must have an SSH tunnel on port 4190 to the webserver.
In addition a default script is provided in
/var/lib/dovecot/sieve/default.sieve which will filter mail flagged as Spam into the Spam folder. Specifying custom filters will override the default. If you modify the default script on the server, it must be compiled using the
Dovecot acts as an IMAP server, which can be accessed using this HowTo. Authentication is provided using the system's authentication system (ie PAM) and for some reason it is configured to use the ystv.york.ac.uk certificate instead of the ystv.co.uk one.