How to Archive Mozilla Thunderbird Mail Folders

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Updated December 06, 2019

Add a big "Archive" folder or one for every year, and all your messages are quickly available without slowing down your everyday email handling. Of course, you want to back up mail, in particular, the messages that have been worthy of keeping in the first place.

Archive Mozilla Thunderbird Mail Folders

Combine backing up local Mozilla Thunderbird folders with cleaning up and archive old mail remotely.

Close Thunderbird and go to your Mozilla Thunderbird profile directory.
Open the Mail folder.
Look for the file named like the Mozilla Thunderbird folder you want to archive in the Local Folders or an account-specific sub-folder (such as pop.gmail.com, for example).

Make sure you pick the file that has no extension not the identically named file with the .msf extension. (For example, Archive is correct but Archive.msf is not.)
Drag and drop the files to the desired archive location (on a removable medium such as a DVD, an external hard drive, a network drive or internet storage, for example).
Open Mozilla Thunderbird.
Delete the folders whose corresponding files you have just copied to the archive location.

Open Archived Mail

Make sure Mozilla Thunderbird is not running and access the archived folder via the profile directory.

Open your Mozilla Thunderbird profile directory.
Go to the Mail folder.
Drag and drop the archived folder file (Archive, for example) from its remote location to the Local Folders folder.

Make sure you do not overwrite existing files. If a file with the same name already exists under Local Folders, rename the archived folder file before copying.
Open Mozilla Thunderbird.
The archived folder should appear under Local Folders in the folder list.