isync is a command line application which synchronizes mailboxes; currently
Maildir and IMAP4 mailboxes are supported. New messages, message deletions
and flag changes can be propagated both ways. isync is suitable for use in
Synchronization is based on unique message identifiers (UIDs), so no
identification conflicts can occur (as opposed to some other mail
synchronizers). Synchronization state is kept in one local text file per
mailbox pair; multiple replicas of a mailbox can be maintained.