cPanel's Exim based mail delivery will (optionally) replace MBOX mail storage format with qmail's MAILDIR format, to speed things up in mail servers.
Houston, Texas - November 9, 2005 - cPanel, a leading Web Hosting Control Panel Software provider, officially announced their plans to migrate their products to support maildir mail storage format. Maildir mail storage format was originally implemented on qmail to address the shortcomings of mbox. Maildir mail storage speeds up the functionality of the mail server and reduces memory usage due to mail related processes. Keep reading for more information about mbox vs. maildir.
If users have any concerns about migrating their servers to maildir format, we recommend contacting cPanel support to address any concerns they may have. As a result of this conversion, Neomail will not function and it is recommended that server administrators migrate their clients to either SquirrelMail or Horde before converting to maildir format. Please note that custom configurations related to email may be affected by this change.
cPanel is a leading Web Hosting Control Panel Software provider supplying hosting automation tools to numerous data centers and customers all around the world. cPanel offers web hosting software that automates the intricate workings of web hosting servers. cPanel products are used on tens of thousands of servers worldwide to equip server administrators with the tools they need to provide top notch hosting to their customers.
About MBOX mail storage format
This is the traditional way to store mail on UNIX-based mail servers. Individual messages are simply concatenated together, and saved in a single file. A special marker is placed where one message ends and the next message begins. Only one process can access the mbox file in read/write mode. Concurrent access requires a locking mechanism. Anytime someone needs to update the mbox file, everyone else must wait for the update to complete.
About MAILDIR mail storage format
Maildirs were originally implemented in the qmail mail server, supposedly to address the inadequacies of mbox files. Individual messages are saved in separate files, one file per message. There is a defined method for naming each file. There's a defined procedure for adding new messages to the maildir. No locking is required. Multiple processes can use maildirs at the same time.
So, why MAILDIR over MBOX?
There could be several reasons, to put things in perspective here's a quote from the Courier's "Benchmarking mbox versus maildir" final analysis:
"Maildirs will not scale very well on servers that use old, slow, hardware. Maildirs will also do poorly with an inefficient filesystem that stores very large folders which are frequently searched for specific content. However maildirs' performance should be adequate even on slow machines with very large folders, as long as the mail activity is just occasional read/write access, and browsing. Even with large folders, containing unread messages, maildirs will require less system load than mboxes".
"On fast hardware, these benchmarks indicate that maildirs scale better in more often than not. Maildirs scale much better with mail folders that contain large messages. Even with folders that have a large number of smaller messages, maildirs did better than mboxes on many benchmarks".
"The final conclusion is that -- except in some specific instances -- using maildirs will be just as fast -- and in sometimes much faster -- than mbox files, while placing less of a load on the rest of the mail system".
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