There are lot of Imap servers that support qmail and vpopmail.
- Courier-IMAP is a qmail, Maildir, and vpopmail compatible IMAP server, with multiple authentication methods. Courier-IMAP is a popular solution.
- Andreas Aardal Hanssen has written Binc IMAP. It works with qmail, vpopmail, or any other checkpassword compatible authentication system. Binc IMAP was created to provide IMAP functionality to qmail.
- David Summers has a qmail-imap GNU/Linux RPM. This is a version of the IMAP/POP server that works with qmail, using Mattias's patches. The three differences are:
- Mail is delivered to and picked up from ~user/Mailbox
- Mail can be delivered to and picked up from ~user/Maildir/ (see README.maildir)
- CRAM-MD5 authentication has been added to the IMAP server.
- Mattias Larsson wrote a preliminary patch to IMAP4rev1 which lets it work with Maildirs. David Harris has improved that patch to make a production quality UW-imap server with Maildir support. And in his turn, Herbie has updated the Maildir patch for the latest UW IMAP server.
- minimalistic dovecot imapd. Dovecot is minimal but feature rich and secure, it should be enough for anyone. Maildir++ quota is not currently supported in dovecot. If you need quota, use Courier-IMAP.
Any maildir aware imapd should work with qmail. For vpopmail support with an IMAP server not specified above, some customization may be needed.
Commonly known compatibility problems:
- Some versions of Outlook have problems with Courier-IMAP. It might be fixed in newer versions
- Note that Microsoft usually produces code with broken implementation of all protocols
- There are also lot of broken IMAP implementations on mail clients, some bugs are fixed in servers, some are not. Do not always claim that server is broken, usually broken stuff is in client