User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.8.1.6) Gecko/20070725 Firefox/2.0.0.6 Build Identifier: version 2.0.0.6 (20070728) If you check "Allow anti-virus clients to quarantine individual incoming messages" in Tools : Options : Anti-Virus then "Delete from POP Server" will not work in Message Filters. Reproducible: Always Steps to Reproduce: 1. Install Thunderbird on two machines with the same user account. 2. Check "Allow anti-virus clients to quarantine individual incoming messages" on both machines. 3. Create a message filter on both machines to delete messages from the POP server whose subject line contains "Not Deleted From POP Server". 4. Send a message to yourself with "Not Deleted From POP Server" in the subject line. 5. Still at the first machine, download messages to receive the message you have just written to yourself. 6. Go to the other machine and download messages again. You will be disappointed to see that the message was not deleted from the POP server. Actual Results: Filtered messages are not deleted from POP server. Expected Results: Filtered messages should be deleted from the POP server. You should only be to download them on the first machine, not again on the second machine. The relation between anti-virus quarantining and not removing messages from the POP server was pointed out by David Bienvenu in a comment to Bug 370442.

Marking NEW per bug 370442 discussion.

Is still here on Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.9.1.5pre) Gecko/20091023 Lightning/1.0pre Shredder/3.0pre ID:20091023031634 Bug #507090 can't fixed :-(

It seems that this is closely dupe of bug #315791. Feel free to reopen it if I'm wrong.