MailFundusMove Apple Mail to an external drive
October 2026 · about 4 minutes to read
In short: Apple Mail has no option to keep its data on another drive, and moving the folder by hand is risky. The safe way: back up old email into an archive on the external drive, have it verified, and only then clean up in Mail. Everything stays searchable, and your Mac gets its space back.
What Apple Mail can do on its own
Mail keeps all messages and attachments in the folder ~/Library/Mail on the internal drive. There is no setting that moves this folder to an external drive. What Mail does offer:
- Export a mailbox. Mailbox > Export Mailbox… writes a mailbox as an .mbox file, also to an external drive. You can then delete it in Mail. To search the file, though, you have to import it back into Mail.
- Leave messages on the server. With IMAP accounts your email lives with your provider anyway. That only helps while there is enough space there, and it does not protect you if something gets lost at the provider.
Why you shouldn’t simply move the Mail folder
Some tutorials suggest copying ~/Library/Mail to an external drive and replacing it with a link. Apple does not support this. If the drive is ever not connected, Mail can no longer find its data, and if something goes wrong there is no supported way back. For your most important correspondence that is a poor trade.
The safe way: archive to the external drive
- Create an archive on the external drive. An archive is a single package file that you can later copy wherever you like.
- Back up the old mailboxes into it, for example everything older than a year.
- Have it verified that every message arrived completely.
- Only then remove the backed-up messages from Mail. Newer email stays where it is.
Keep in mind: whatever you then clear out of Mail exists only in the archive. It is not a copy, it is the original. Back up the external drive as well, for example with Time Machine or a second copy.
How MailFundus Archive does it
When you set it up, you choose where the archive lives. An external drive is just as good as your Documents folder. MailFundus Archive backs up the selected Apple Mail mailboxes there, attachments included, and verifies every message byte for byte. Nothing is moved or deleted without your OK. Only if you choose to, the verified messages go to Mail’s Trash, which you empty yourself.
With the drive connected, you find any message in milliseconds, even by what is inside PDF attachments. Single messages or whole mailboxes come back into Mail as .eml or .mbox. Because the archive only ever adds new data, Time Machine backs up only what is new on each run.
Free for up to 500 messages, with every feature. The full version is US$24.99 once, no subscription (price varies by country).
Free for up to 500 messages: get it on the Mac App Store