CompactOnDelete is a Mozilla Thunderbird 2.0 and 3.0 extension that schedules IMAP folder compaction to happen when Thunderbird loses its window focus or closes after messages are removed from an IMAP folder. Only those folders with removals are compacted; other folders are left alone. This is meant to automatically make deleted messages disappear from Outlook and Outlook Web Access on an Exchange server when they are deleted in Thunderbird. Other IMAP servers don't need this extension, and the use of this extension limits your ability to undo as soon as Thunderbird loses its window focus, since compacting a folder clears the undo/redo history.
A future enhancement could involve detecting which IMAP servers are Exchange and compacting only their folders on Thunderbird's focus loss. Presently, this extension will compact any IMAP folder that gets messages deleted or moved away from it. This extension now compacts the folders that a focus loss would have compacted when Thunderbird is closed, though it presently does not work if the user uses File | Quit instead of closing the window.
CompactOnDelete is distributed under the terms of the GNU General Public License (GPL), version 2, and is copyright (c) 2008-2010 Steven Lawrance.