The wording that is used can help work out what is going on. If you see the word 'SPAM' then it is not Thunderbird. This could be the server using eg: 'Spamassassin' and marking the message. In your Junk Controls, perhaps you have instructed Thunderbird to 'trust junk mail headers by eg: Spamassassin'. You can uncheck that in the mail accounts Account Settings > Junk Controls. This does not stop emails being marked a spam, but it does mean Thunderbird will not act on it, so emails should not get moved to Junk folder. If you see the word 'Junk' then it is Thunderbird Junk Controls. I'm presuming you have set up your Junk Controls for the account and global options. Suggest you make sure the email address in in one your address books and that address book is selected as a whitelist. * https://support.mozilla.org/en-US/kb/thunderbird-and-junk-spam-messages If you see the word 'Scam' then this could also be Thunderbird. This is flagged when an email contains common techniques used to deceive you. You will see a red warning on the email with an 'Options' button. You can use the drop down options to choose whether to 'ignore the warning' or switch off this auto detection process. In 'Options': * Under 'Security' > 'Email Scams' tab: * uncheck 'Tell me if the message I'm readidng is a suspected email scam' * click on 'ok'