Perhaps the problem is you are having trouble with the precedence of how messages are filtered.

First thing is filters only work on mail that is in the folder, so if the first action marks the message as junk, and you have automatically move junk to the junk folder, then that is where the filter processing will end as the message is no longer in the folder to be further processed to get moved to junk.

So you mark it as junk and it goes to junk where it is subject to whatever junk processing you have in your account settings. Like being auto deleted after XX days.

Fundamentally you just can't delete and mark as junk in a single filter, because both actions by default result in the mail leaving the folder at that point so whatever follows fails.

Thank you, Matt. In no filter do I have action to mark as junk.

It occurs to me that perhaps these messages arrive already tagged somehow as junk, and TB acts accordingly without applying filter. What do you think?

It occurs to me that perhaps these messages arrive already tagged somehow as junk, and TB acts accordingly without applying filter. What do you think?

If you have an imap account then any email the server marks as junk/spam will auto get put into the server Spam folder. Thus ends up in your imap account spam folder. Message Filters created by you in Thunderbird cannot act on that email because it's not arriving into the Inbox.

There is a setting in 'Account Settings' > 'Junk Settings' which can auto put emails arriving in Inbox into Junk. If checkbox is selected for :'Trust junk mail headers set by: x'. So I suggest you check to see if that option is selected and uncheck/deselect it.

You can tell if server or Thunderbird marked something as junk which may help in understanding the problem. In Folder Pane: Select Junk/Spam folder Enable the column header called 'Spam' If the flame icon is red then it was marked as junk either by Thunderbird Junk filter or by you performing it manually. If the flame icon is just an outline - not red - then it was marked as junk by server.

@Toad-Hall, thank you for the good reply.

Since I posted my thought about pre-junked messages, I have been able to make TB automatically delete nearly all of them : In header that is titled "X-Microsoft-Antispam-Mailbox-Delivery", at end of its longish content there is text "JunkEmail". I filter on that header and that text, action to delete.

I always have had unchecked the option "Trust junk mail headers set by".

I like your information about the column titled "Spam", and I enabled it just now.

Addendum

> there is text "JunkEmail"

Is either present or absent at end of string.

> "If the flame icon is just an outline - not red - then it was marked as junk by server."

Perhaps same as the uniformly colored gray icons that I get?