Betterbird: Downloads

History: In December 2023 the Thunderbird team greatly changed the internals of mbox file handling, introducing a number of regressions. Soon after, the first bug was filed, reporting IMAP folder corruption. Currently, this bug is tracking the issue.

Symptoms: IMAP folder corruption is easy to notice. The user clicks on a message, and the message isn't correctly display. Usually some raw message content is displayed, often a MIME boundary starting with --. Some users report that a different mail from the one that was clicked on in the message list is displayed. Note that since the Thunderbird folks forced version 128 onto unsuspecting users via an unnecessary update, they are getting a high volume of reports that people's e-mail can't be displayed any more.

Remedy: Repairing the affected IMAP folder (Right-click, Properties, Repair Folder) usually fixes the issue. That's fine for users with little data, it causes problems for users with large folders (more than 1 GB) since the repair downloads all messages again. Some Thunderbird users report that they need to repair they IMAP mailboxes multiple times per week.

Outlook: We were estimating that the problem would be fixed in version 128.3.0 due in October 2024, but the Thunderbird team have done precious little to address the issue. It is possible that 128.3.0 will still be defective. That would leave Thunderbird and Betterbird users in the precarious situation that they will need to switch to and unstable version in October, since version 115.15.0 will reach "end of life" status when 128.3.0 ships. We thoroughly regret this situation.

Get in touch: If the IMAP folder corruption is affecting you, please get in touch with our support team, and we will work through the issue with you.