And you would be using a yahoo account I guess. Sounds exactly like their behavior at least. Do the junk mails have a red icon in the junk column, or is it black and white? Thunderbird marks junk with the red icon. Servers do not. So checking that provides a starting point.

Are you using the latest version of Thunderbird? There was a bug that was fixed a year or two ago with regard to how Thunderbird marked junk as junk that could also result in what you are seeing.

Hi.

I'm using protonmail. In the preview column with the other junk emails, the T-bird junk icon looks like an orange flame outline over white. When you open it, the icon becomes black flame outline. So far the problem is only with 2 emails, sent by me.

I have an att.net account too, but I haven't had this problem with it.

I have 78.14.0 (32-bit), appears to be the latest.

Thank you

open it? the icon is red for Thunderbird determined spam and a black outline for not spam. But of course we are dealing with a local implementation of an IMAP server in the proton mail briodge, that uselessly adds complexity. Thunderbird will not mark mail from folks in your address book as junk if the address book is listed and selected in the account junk settings.

I don't know what you mean by "open it"?

Select 'Spam' folder to see list of emails in the 'Thread Pane' If the 'Junk Status' column header is enabled then each email in the list will have either a yellow flame with orange border or a grey outline of a flame which has either dark or light flame depending upon theme. If it is yellow/orange flame then Thunderbird marked it as Junk.

Thunderbird will mark as junk if junk filters say email looks like typical junk content where Junk Filter has been trained by you to say that email is junk or you have created a Message Filter to say mark it as Junk OR it will mark as junk and put into the Spam folder if you have the Account Junk Settings selected to Trust junk mail headers set by another filter eg: SpamAssassin

If you say those emails were your own email address then make sure you are listed as a contact in the Personal Address Book and also make sure your address books are whiltelisted in the account Junk Settings.

Example of Junk Settings image below.

However, it is also highly possible the protonmail server is putting those emails into the Spam folder because it has it's own spam detection filters. When Imap Spam folders synchronises/downloads from server then thunderbird imap account will display whatever is already set on server. This info may be helpful to try to get more control over the server filters. https://protonmail.com/support/knowledge-base/spam-filtering/

In Spam folder If you click on an email in the list so you can read the contents in the lower Message Pane (or double click to open inj a new tab) - in other words open the email -

Do you see a Message on yellow background that says : 'To protect your privacy, Thunderbird has blocked remote content in this message' If yes, then this email was set as junk by the server.

Or do you see this message: 'Thunderbird thinks this is Junk mail' If yes, then Thunderbird marked it as Junk.