Courier-IMAP is a server that provides IMAP access to Maildir mailboxes.
This IMAP server does NOT handle traditional mailbox files
(/var/spool/mail, and derivatives), it was written for the specific
purpose of providing IMAP access to Maildirs.
Courier-IMAP implements some extensions to the basic Maildir mail
storage format in order to support some additional features, such as
folders and “soft” quotas. This is done in a way that’s backwards
compatible with the standard Maildir users (although, of course, they
will ignore the additional features). Other software that understands
and uses the same Maildir extensions is SqWebMail, and maildrop.
* Extremely small footprint.
* Abstract authentication modules.
* Virtual mailbox support.
* Pop3 daemon.