following is a problem that we have been trying to solve for a while now...

we are attempting to archive a couple of rather large mail folders from within apple mail, they contain in excess of 20000 emails and the actual folders in...


... are around 14GB in size.

the problem is that if we archive these from within mail, the export only generates mbox files of around 4.2GB, which do not contain all emails from the original folder.

is this a known limitation of the mbox format or more likely apple mail?

the obvious alternative to the above approach is to directly backup / archive the actual mbox folders in ~/Library/Mail/Mailboxes?


2 Answers 2


I'll assume your mac is running on HFS Plus - the default file system - and in that case, the limitation is clearly the Mail application and not a file size limitation. Mbox files are just text files, so there's not much going on in them. You'll need to follow your alternative and back them up from finder or consider moving them to a Lion mac to see if this issue is corrected there.

According to the Mac OS Extended format (HFS Plus) volume and file limits KBase article, a 2 GB file and volume limit existed from OS 10.0 to 10.1.5 and was raised to 8 GB from 10.2 to 10.2.8.

In your case on Snow Leopard (and any OS 10.4 or newer) - the file size limit is 8 exabytes.

Stop here unless you want all sorts of silly storage calculations that don't really apply since you'd need 2.6 million 3 TB drives to make this amount of real space.

8 EB is eight million terabytes. This insane amount of storage would list price cost $480 million for the hardware alone if you ran BackBlaze storage units.


I have successfully archived mbox folders in excess of 10GB using MailSteward.

The program puts mail into a SQLlite or MySQL (depending on the version) database, archives attachments, and allows archived mail to be easily tagged, searched, accessed and replied to/forwarded etc.

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