Automatically Remove Old Mail in Mozilla Thunderbird

A Trash folder is a wonderful thing to have to recover messaged deleted by accident, but even the trash must not grow indefinitely. Of course, you can always empty the Trash folder manually in Mozilla Thunderbird. This, however, deletes all messages in it immediately, and emptying the trash is really something your software should do for you.

Mozilla Thunderbird does and does it in exquisite a manner.

Instructions in this article apply to Thunderbird 68 or higher on Windows 10, 8, or 7; Mac OS X 10.9 or higher; and GNU/LINUX.

Remove Old Mail Automatically From a Folder

You can configure Thunderbird to delete old messages in every folder in Mozilla automatically. What is useful for the Trash folders is also great for RSS feeds, for example.

Right-click the desired folder.
Select Properties from the menu.
Go to the Retention Policy tab.
Make sure Use server defaults or Use my account settings is not checked.
Select either Delete all but the most recent __ messages (or Delete all but the last __ messages) or Delete messages more than __ days old.

Typically, make sure Always keep starred messages is checked; this allows for an easy way to preserve emails.
Enter the desired time or message count.
- Keeping about 30 days or 900 messages in a Trash folder usually works fine.
- Even for something like your default inbox, 182 days (around 6 months) can work.
Select OK.

Remove Old Mail Automatically for an Entire Account

To set a default policy for an account that has Mozilla Thunderbird delete old emails across folders in the account:

Select Preferences > Account Settings from the Mozilla Thunderbird menu.
You can also select Tools > Account Settings (Windows, Mac) or Edit > Account Settings (Linux) from the menu.

For local folders and POP email accounts:

Go to the Disk Space category for the desired account (or Local Folders).

For IMAP email accounts:

Go to the Synchronization & Storage category for the desired account in the Account Settings window.
Make sure you checked Delete all but the most recent __ messages or Delete messages more than __ days old.
If you are prompted:
Select OK in the Confirm permanent, automatic deletion of messages dialog.
- Do keep in mind that messages you did want to keep may inadvertently be deleted with this setting; do, perhaps, not rely on your starring messages to retain them.
- At the same time, chances are you will not miss any messages older than, say, a year that have been permanently deleted.
- You can adapt the default settings for any individual folder to either keep more or less mail or to turn off automatic deletion altogether; see above.
Click OK.