I'm administering two mail servers (Debian Sarge) and uw-imapd were running on both servers. As you know uw-imapd is reference model and may become very slow when user has a huge mbox. I use "mobileimap" to see my IMAP from cellphone, but huge mbox sometimes causes bad timeout. Courier-imapd is dropped from the choice, because I don't want to migrate other formats. My friend Kitame and Mutsumi recommended 'dovecot-imapd'. Yeah, this is what I want. Install was very smooth, but there was one problem. I'd like to use CRAM-MD5 for authentication mechanism, but I couldn't find a way to create its hashed value to write password file. After asking Google and checking unstable dovecot-common, finally I found "dovecotpw" utility and succeeded to get correct hashed value by using this utility on other Debian Sid machine. Now dovecot works well on my two servers. Speed is more faster than I imagined.