niekvs (1031964) writes "Ever since Thunderbird's latest update (184.108.40.206) was released a few weeks ago, a very nasty bug was introduced - and sadly enough the Mozilla team isn't hurrying to release a patch, leaving millions of users exposed. I noticed this problem by accident, when i realized that Thunderbird was downloading far more mails than were showing up in my inbox. The first few days i wasn't paying much attention to it, because sometimes 70% of my mail is automatically redirected to my spam box anyway, but at some point i started actually counting the mails by hand and found out that a large portion of mails just didn't show up, even though they were downloaded. I then followed Mozilla's recommended practice of compacting my mailboxes, to no avail. Desperate, i searched Google for help, and found out that a lot more users were experiencing similar issues (1) (2) with the latest update. The bad thing: compacting actually permanently deletes the missing messages (that are likely mostly spam, but can also be legit). If you haven't done this yet, you should downgrade back to the previous version, 220.127.116.11, exposing yourself to some security issues, but at least having peace of mind that you receive all your mail, and won't receive any angry mails from friends or colleagues asking why you haven't returned their important questions yet. Please read the comments in the bug report for more information. This issue seriously broke my confidence in this program, especially considering that Mozilla appears in no rush to release an update, and are still distributing the buggy version weeks after discovery. In my opinion, this is a much more serious problem than whatever obscure security bug they were trying to fix in this version. Most people probably won't even realize something is wrong, because the mails simply never show up..."