Install the Mac OS X Server v10.6.2 Update or later, then enable SSL as described in Mail Service Admin Guide.
In Mac OS X Server v10.6 and v10.6.1, you can enable this feature by modifying the dovecot.conf file after enabling SSL in Server Admin Mail.
- Open the /etc/dovecot/dovecot.conf file in a text editor.
- Look for the ssl_ca_file key. It will look something like this:
#ssl_ca_file = /etc/certificates/example.host.com.F0715C4FE6E120BBCC51EAC854DB73E9686D4DD2.chain.pem
- Remove the # character, so that the key begins like this:
ssl_ca_file = ...
- Save the file.
- Restart the mail service.