Thunderbird Labels Messages as Spam Incorrectly

Have you seen https://support.mozilla.org/en-US/kb/thunderbird-and-junk-spam-messages ?

I have. Unfortunately, it does not provide a way to ensure that Thunderbird doesn't identify my subscriptions and necessary emails as spam. For example, certain business-related emails are labeled spam.

Thunderbird doesn't identify my subscriptions and necessary emails as spam.

I've been having this issue myself for months now. My subscription emails are forwarded through some of my relay addresses and are always sent directly to the spam folder. Do you have any spam filters enabled, and if so what does your filter log say whenever you look in your spam folder? My filter log has been blank despite my spam being full of valid emails that have filter rules set for them, and I think it's some weird situation of filters not applying to incoming emails.

I've asked a similar question here and gotten two responses: update filters to run "before spam classification" (I've had this set for months already), and the second was to just keep clicking "not spam" on my messages to train the filter. I'm at 88 manual "not spam" clicks for my news emails alone at this point, and the issue is not even remotely improving which really makes me think (again) that something is broken or just not working properly. I hope you can get help and a fix to your problem. Right now I think my post has been abandoned so I'm really hoping devs or whoever can come through for you on this.

I have. Unfortunately, it does not provide a way to ensure that Thunderbird doesn't identify my subscriptions and necessary emails as spam. For example, certain business-related emails are labeled spam.

Do the messages have a flame in the spam column of the message list?

At least some do have the flame symbol. Unfortunately, because Thunderbird makes this assumption, I have to go through all those messages individually and mark them as Not Spam. I have thousands of emails, and going through even 50 or 100 mislabeled messages is not something I want to have to make time for every day or so.

On the other hand, Thunderbird doesn't flag commonly-used gibberish email addresses as spam!

At least some do have the flame symbol. Unfortunately, because Thunderbird makes this assumption, I have to go through all those messages individually and mark them as Not Spam. I have thousands of emails, and going through even 50 or 100 mislabeled messages is not something I want to have to make time for every day or so.

• Messages that do not have the flame symbol were not put in the spam folder by Thunderbird. Therefore, marking these messages as not spam in Thunderbird does nothing to improve how these messages are handled. IF your mail provider a) trains their spam handling based on you manually moving them back to the Inbox, then that is your best course of action, b) allows you to mark messages as not spam in their web interface then use that. If they offer neither capability, then you need a better provider.
• Messages that do have the flame can be marked as not spam, which will train Thunderbird's system. But it is not a guarantee. To guarantee a message won't be changed to spam by Thunderbird you need to use combination of whitelist and filters which is documented in the KB article.

On the other hand, Thunderbird doesn't flag commonly-used gibberish email addresses as spam!

Thunderbird does not have modern spam capabilities that many mail providers offer today. You will want a mail provider who offers modern capabilities.