kashani
Ran into some issues updating to courier-imap-4.0.6-r3 on my VPS so I
decided to take the plunge and go straight to 4.5.0 which is unstable.
4.5.0 is much faster and Thunderbird barely registers email in the Inbox
before the messages are moved to the appropriate folder. My installation
is also a combination of cyrus-sasl, authdaemon from courier-authlib,
Mysql based virtual accounts, ssl certs for imap and smtp, and Postfix.
No changes were needed in courier-imap config files other than restoring
imap.conf settings.
I don't think Courier-imap is faster than Dovecot based on other
people's experience, but has rather reached speed parity with it. If
you're already on Dovecot and happy, stay, if you've been thinking about
Dovecot but have a complex system to move I'd recommend trying the
upgrade to 4.5.0.
I also update gamin and use +fam with courier-imap which might affect
the overall speed. The update from 0.1.9 to 0.1.10 doesn't look like it
would account for the increased speed.