How do I set up Thunderbird so that no incoming email is automatically diverted to my spam folder?

See the <Settings | Privacy & Security | Spam> and uncheck the "When messages are marked as spam: Move them to the account’s Spam folder" option. These are the default settings. They can be overridden by the options in <Account Settings | Spam Settings | Destination and Retention>.

Keep in mind that your email provider may have their own spam rules that move messages to their Spam folder before Thunderbird ever sees them. You can't control that in Thunderbird, but there may be settings for it available on their webmail page.

Thanks for your reply, Lin. Your instructions are very clear. I appreciate that.

My global spam settings were set for "When messages are marked as spam, delete them."

The account spam settings for each of my email accounts are set so that the box next to "Move new spam messages to:" is not checked.

But incoming emails still end up in my spam folder, including a lot of emails that aren't spam.

In global spam settings, I unchecked the box next to "When messages are marked as spam:"

I hope that will prevent emails from getting sent to my spam folder.

Do you think that will work? Is there any other change I can make to my settings to prevent emails from going to the spam folder?

Thanks Clint

Well, you could set up a filter that selects all mail and set the spam setting to 'not spam'

Those settings should work. My recommended settings should have resulted in spams being marked as spam, but remaining in the Inbox. If they are still ending up in the Spam folder, that makes me suspect that your email provider is moving them before Thunderbird fetches mail, as I suggested above.

That's a little tricky to test - you will need to check your email on the provider's webmail page BEFORE Thunderbird checks for new mail. You could temporarily turn off that account's automatic checking for new mail (see the options at <Account Settings | Server Settings | Server Settings> and uncheck "Check for new messages at startup" and "Check for new messages every [x] minutes", and "Allow immediate server notifications when new messages arrive". You can still fetch new mail by clicking the "Get Messages" button, but wait a until you check webmail Spam. After the test, re-enable the three Server Settings.

If you find, as I suspect, that your provider is doing the deed, you will have to consult them to see how to deal with their over-aggressive spam filter system. Some will let you mark messages as "not Spam", some may let you turn it off entirely (not likely), some will let you create a white list of addresses you trust.

Interesting suggestion, David, but...

It's helpful for email to be marked as suspected spam when it lands in my inbox – especially for my first email check of the morning. I can quickly check the emails marked as suspected spam and either tag them as "Not Spam" or delete them. After that I can start going through the overnight emails that are legit.

Thanks again, Lin.

Your recommended settings were how I had TB set up already. You may be right about my domain host tagging emails as spam. I'll ask them about that.

For now, I'm comfortable with how I have the settings. If an email in my inbox is spam, I do two clicks - on the Spam button and on the Delete button. Those buttons are next to each other, so it's quick.

Thanks to you and David for your suggestions.

You may well not be able to prevent mail being placed in the SPAM folder, providers like Yahoo, Outlook and Gmail do not offer automated opt out for their spam filtering or where the mail goes when it is identified as SPAM.

Your issue is most likely your mail provider deciding what is spam completely unrelated to Thunderbird or your settings in it.

Thanks for your reply Matt. Lin had the same thought - that my email provider may be flagging incoming mail as spam, causing it to get diverted to my spam folder. And it looks like you two might be right.

After changing my TB settings to be as sure as possible that TB won't automatically divert any incoming mail to spam, I'm still finding emails in my spam folder. The prime culprit seems to be gmail, but a few emails sent through my domain host are also ending up the spam folder.

Next steps: Ask Claude or Gemini if there's a way to prevent gmail from marking mail as spam, and calling my domain host and asking the same thing.