Received Address book contact goes to 'spam' folder

Thunderbird has a few features to help mitigate spam. You don't mention which you use, if any. Here's an article describing them and how to use them:

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

- If you haven't already, confirm that the replyer's address is exactly the same as what's in your address book, and make sure the setting in <Account Settings | (account) | Spam Settings> is set up properly, including that the Adaptive Spam Controls are enabled.

- pay attention to the section in the article that stresses that you must train the database both what IS spam and what IS NOT spam.

- Consider creating a message filter for this one contact that will explicitly Set Spam Status to "Not Spam".

Thanks for replying 1) Spam / Junk settings: Global Junk settings had already been set per guide 2) Per account settings: Had already been set per guide – white listing ‘address book’ – which includes the email contact in question 3) Yes – Have verified that the email contact’s email address in my ‘address book’ and the reply I get are 100% the same 4) Yes – Have clicked on “not spam” every time I get his email replies, that said, until I read the guide I didn’t know to try and click on the ‘red’ icon, will try that next time, OR, pressing shift+J on the keyboard

Slightly related, I get a “lot” of porn spam. Don’t know why, I don’t go to any of that type of sites. Any way to block them before I get them in the spam folder.

I just ‘now’ turned on the “Spam Assassin”, hope this helps.

Any other suggestions?

It could be that your mail provider rightly or wrongly considers this to be spam and is moving it to the Spam folder before you ever download it. You could verify this by checking web mail before fetching to Thunderbird. The provider may also have its own filtering or whitelisting features.

As a test you could disable all Thunderbird spam controls and observer what happens with this particular contact. If it still ends up in Spam, that would support the above theory.

It's possible that Thunderbird's Adaptive Filtering's database is corrupt. You can reset it at <Settings | Privacy & Security | Junk | Reset Training Data>. This would require you to train it all over again from scratch, so maybe do this as a last resort.

The porn spam will be hard to control unless there is a specific common trait they all share. Possibly a filter with a list of naughty words in the Subject might work, but I bet a lot would slip through. Spammers have tricks to get around filtering on literal criteria. The Adaptive controls are the most effective tool for that, though of course, it can never be 100%

My observation is that spam comes in waves. It will ramp up for a while, hit a peak, then fade away until the next campaign. I deal with it the best I can with the available tools and live with what's left.

Spamassassin depends on if your email provider uses it and if you trust its decisions. If it doesn't offer that service, turning it on in Thunderbird will do nothing, though it won't hurt anything, either. I guess it can't hurt to try.