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When I upgraded to Lion, 5.0 created a directory ~/Library/Mail/Mail Lost+Found. There were a couple of outdated bundles, which seems logical. But there is also a Mailboxes directory that has a lot (~30-40) .mbox files. Here is the contents of one of those files:

total used in directory 224 available 282057236
drwxr-xr-x   6 kmm  kmm     204 Aug  1 15:55 .
drwxr-xr-x  17 kmm  kmm     578 Aug  2 08:47 ..
-rw-rw-r--   1 kmm  kmm       0 Nov  6  2007 .index.ready
-rw-rw-r--   1 kmm  kmm  109793 Nov  6  2007 Incoming_Mail
-rw-rw-r--   1 kmm  kmm    1860 Nov  6  2007 Incoming_Table_of_Contents
-rw-rw-r--   1 kmm  kmm       0 Nov  6  2007 mbox.SKindex.isValid

Is it safe to delete these files? I haven't opened them all to determine if any contains actual messages. The few I have opened have not.

They only occupy 9.5 mb in total, which isn't much, admittedly. But I have something against cruft hanging around when it's not needed.

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up vote -1 down vote accepted

The lost+found folder is a special UNIX folder created for a variety of reasons: Most often the lost+found folder is created after a forced shutdown or a power cut. The OS loses track of what was going on and instead of dumping any files or folders it has lost track of, it puts them in the lost+found folder.

It's not much to be concerned about , seeing as those are some old files they can probably be safely deleted.

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It is possible that these files have existed for a long time. I hadn't looked in ~/Mail recently -- not until I upgraded. – kmm Aug 2 '11 at 21:12
This is not that folder! Repairing a HFS filesystem doesn't generate a lost+found, and the name indicates that this one was probably created by Mail. It is probably named after the traditional lost+found and serves a similar role of collecting misplaced files, but I highly doubt it actually stores files lost due to filesystem corruption. – Kevin Reid Oct 16 '11 at 13:00

This folder is created by Mail when updating to Lion. I don't think it indicates any problems with a forced shutdown. It's just a place to store the old files after Mail has migrated to its new folder structure in the ~/Library/Mail/V2 folder. If the update is successful, you shouldn't need anything in this folder, except perhaps the contents of the Bundles folder if you want to re-install any plug-ins.

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