configsaver is a small commandline utility written in Python that will synchronize the files you specify using your gmail account.
synchronizes mailboxes between two imap servers
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 IMAP-disconnected mode.
a utility for Maildir-synchronization. It is designed to be used in online (live) maildir folders, be fail-safe and optimized for minimal bandwidth
a way of synchronizing a collection of mailboxes. The algorithm is a 3-way diff. Two mailboxes are simultaneously compared to a record of the state of both mailboxes at last sync
mswatch is a command line unix program that keeps two mailboxes synchronized more efficiently and with shorter delays than periodically synchronizing the two mailboxes.
a tool to simplify your email reading. With it you can read the same mailbox from multiple computers and have your changes be automatically reflected on all computers. You can use various mail clients to read a single box or read mail while offline with full synchronization when you reconnect
Zapmail is an efficient e-mail synchroniser, designed for rapid transfer of small changes to a large quantity of mail. It allows you to store two or more copies of your e-mail, change them (e.g. by reading or moving mail around on your laptop or new mail arriving on the server), and then merge the changes when the two machines are on-line again so that both copies are up to date.