I exported a mailbox with about 4 GB. The export file name contained the word partial while the size increased. Then, when the exported mailbox reached 2.15 GB, the word partial was no longer part of the filename. So, I assumed that the mailbox was successfully and completely exported.

But I was curious why the exported mailbox was so much smaller in size than what was shown in the Mail app. So I searched the internet and found information about a 2.15 GB limit for exporting mailboxes.

My questions are:

  • Is it really true that the size of exported mailboxes is limited?
  • Why would there be such a limitation? My SSD uses APFS…
  • How can I export my 4 GB mailbox?

If it was indeed the case that this limitation still exists, I would find it very strange that the Mail app does not issue a warning about an incomplete export. I almost lost about half my emails assuming that the export was complete…

  • Was the export complete in that it contained all the messages you expected? Did you check you'd actually lost 'half', or was your loss assumed given the unexpected size? The Mail app may store other metadata in the mailbox, eg indexes, graphics etc. If the export process omits those (it certainly would for indexes I'd imagine), then the exported size could feasibly be smaller. Jan 25, 2023 at 21:57
  • I thought about this, too. But my file size is exactly 2.15 GB, and therefore exactly the number I found on several websites as the maximum export size. It is very unlikely that my mailbox size matches this number by accident.
    – John
    Jan 25, 2023 at 22:03


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