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Automatic folder compaction and #PB# files

In order to reclaim unused disk space, Postbox may compact the per folder "mbox" files that store your email.  Because folder compaction is a resource-intensive operation, Postbox does this when left idle. 

By default, Postbox will only attempt to compact a folder if it will save 100MB of disk space. This preference can be changed in Preferences | Options > Advanced > Network & Disk Space.

When compacting local mail folders (including POP accounts), Postbox will keep a backup of the original folder alongside the compacted version.  For example, if the folder is Inbox, the on-disk backup will be named #PB#Inbox.  Only one backup (per folder) is kept around at any time.  It is safe to delete these #PB# files.

Note that backup files are not made for folders on IMAP accounts (as the server has a copy of the messages.)

To manually compact folders, please select Compact Folders from the File menu.