There is sometimes a bug/error in Thunderbird where it keeps sending some or all of your emails to junk folder. Even if you repeatedly mark them yourself as “not junk,” it has no effect on Thunderbird. Sometimes, manually moving the junk emails to inbox folder can work, but in other cases, Thunderbird will move them back to Junk folders and also flag new emails as junk too.
Thunderbird marks emails as junk
This unexpected behavior with your emails in Thunderbird is due to several reasons. Sometimes, it’s not clear as to why this is happening and it can be hard to pin-point the exact cause. In some cases, it’s not the fault of Thunderbird but the emails are being marked as junk from the server or your email provider. Whatever the reason is and wherever the fault is, below are some troubleshooting fixes that will likely fix this annoying error.
Troubleshooting tip 1: Fix it from server side
Firstly, if you are using an IMAP email account, the chances are likely that this is happening from the server side, not from the client side. Go to your webmail and mark the junk emails as “not junk.” You can also go to the filter settings of your webmail provider and filter all the emails that you think are important but going to the junk folder and create a rule to always send them to inbox.
Troubleshooting tip 2: Delete spam folder
Here’s a slightly rough solution: delete your spam folder, but first make sure all the important emails from it have been moved to inbox or saved somewhere safely. Then create a new spam folder. This sometimes automatically fix whatever conflict or error the previous “Spam” folder might be causing.
Troubleshooting tip 3: Thunderbird’s Adaptive Junk filter feature
Thunderbird has its own adaptive junk filter method that gradually learns what emails to mark as junk, based on when you mark certain types of emails as junk. It also learns what emails to consider as important whenever you mark emails from junk folder as “not junk.” IF you find that Thunderbird keeps sending important emails to Junk, this “training” on adaptive junk filters might be broken or corrupt.
Go to “Tools” à Options à Privacy and security à then go to “Junk” section à and click on “Reset Training Data.”
You can also uncheck the “Enable adaptive Junk filter logging” feature and see if that makes Thunderbird’s behavior suitable to your needs.
Troubleshooting tip 4: Delete training.dat
Sometimes, deleting or resetting training data from Thunderbird’s interface doesn’t quite clear the training information completely. But you can directly this “training.dat” file from the Profile folder, which will force Thunderbird to create a new training.dat file from scratch. This completely resets whatever Thunderbird has learned about spam filters.
First, close Thunderbird, then go to the Profile folder of your Thunderbird, find “training.dat” file and delete it. Now you can start Thunderbird with a fresh new rules and filters for marking emails as spam.
Here are some more quick fixes if the above suggested troubleshooting tips didn’t work for:
- Right click on the “inbox” folder and go to Properties and then click on “Repair Folder.” Repairing folder also resets the old but broken information, which includes all the spam filters and training
- Turn off your antivirus temporarily and see if that fixes the problem. Sometimes, antiviruses can also be the reason behind emails being considered as junk, especially if they have attachments. If this turned out to be the reason for you, you might have to go to your Antivirus settings to fix it.
As in most cases, if the problem seems to persist after trying all those troubleshooting tips, the final solution is to completely reinstall Thunderbird again. But we hope that you don’t need to do that and one of the more simple fixes explained above helps you in getting rid of this annoying issue where Thunderbird keeps marking important emails as Junk.