OfflineIMAP is a tool to simplify your e-mail reading. With OfflineIMAP, you can read the same mailbox from multiple computers. You get a current copy of your messages on each computer, and changes you make one place will be visible on all other systems. For instance, you can delete a message on your home computer, and it will appear deleted on your work computer as well. OfflineIMAP is also useful if you want to use a mail reader that does not have IMAP support, has poor IMAP support, or does not provide disconnected operation.
OfflineIMAP works on pretty much any POSIX operating system, such as Linux, BSD operating systems, MacOS X, Solaris, etc.
OfflineIMAP is a Free Software project licensed under the GNU General Public License. You can download it for free, and you can modify it. In fact, you are encouraged to contribute to OfflineIMAP, and doing so is fast and easy.
OfflineIMAP is FAST; it synchronizes my two accounts with over 50 folders in 3 seconds. Other similar tools might take over a minute, and achieve a less-reliable result. Some mail readers can take over 10 minutes to do the same thing, and some don’t even support it at all. Unlike other mail tools, OfflineIMAP features a multi-threaded synchronization algorithm that can dramatically speed up performance in many situations by synchronizing several different things simultaneously.
OfflineIMAP is FLEXIBLE; you can customize which folders are synced via regular expressions, lists, or Python expressions; a versatile and comprehensive configuration file is used to control behavior; two user interfaces are built-in; fine-tuning of synchronization performance is possible; internal or external automation is supported; SSL and PREAUTH tunnels are both supported; offline (or “unplugged”) reading is supported; and esoteric IMAP features are supported to ensure compatibility with the widest variety of IMAP servers.
OfflineIMAP is SAFE; it uses an algorithm designed to prevent mail loss at all costs. Because of the design of this algorithm, even programming errors should not result in loss of mail. I am so confident in the algorithm that I use my own personal and work accounts for testing of OfflineIMAP pre-release, development, and beta releases. Of course, legally speaking, OfflineIMAP comes with no warranty, so I am not responsible if this turns out to be wrong.
OfflineIMAP traditionally operates by maintaining a hierarchy of mail folders in Maildir format locally. Your own mail reader will read mail from this tree, and need never know that the mail comes from IMAP. OfflineIMAP will detect changes to the mail folders on your IMAP server and your own computer and bi-directionally synchronize them, copying, marking, and deleting messages as necessary.
With OfflineIMAP 4.0, a powerful new ability has been introduced ― the program can now synchronize two IMAP servers with each other, with no need to have a Maildir layer in-between. Many people use this if they use a mail reader on their local machine that does not support Maildirs. People may install an IMAP server on their local machine, and point both OfflineIMAP and their mail reader of choice at it. This is often preferable to the mail reader’s own IMAP support since OfflineIMAP supports many features (offline reading, for one) that most IMAP-aware readers don’t. However, this feature is not as time-tested as traditional syncing, so my advice is to stick with normal methods of operation for the time being.