Project Wombat: Filter Rule Match Page

My message was rejected with the statement “filter rule match”. What does that mean?

This question comes up often enough that we have built a separate page to address it directly.

“Filter rule match” is the generic message which Mailman (the list processing software we use) uses for all automatically rejected messages, regardless of cause. (It would be nice if a future version of Mailman had the option to give custom error messages for different errors, but at the moment they all use the same three words.)

Roughly half the people who receive this error message ask whether we are rejecting their message because of who sent it. The answer to that question is “no”. The “filters” which we use — the word suggests an almost completely inaccurate picture of what Mailman does behind the scenes — almost entirely deal with message formatting, rather than source or content. (We do have a few filters which technically deal with content. For example, we exclude attachments.)

Listed below are the most common things which set off this message, in order of how often they show up.

Incorrect Submission Address
You must send your posts to either or (See the list FAQ for the difference between the two addresses.) Posts submitted to any other address will be automatically rejected by the server. As of this writing, over 80% of the people who have complained about “filter rule match” rejections were using the wrong address.
We use special addresses, rather than the default Mailman addresses, to guarantee that every post is at least submitted to all three lists. If the lists didn’t reject direct posts, then it would be possible for a message to show up on one list but not the others, which would defeat the purpose of having discussion lists.
Base64 Encoding
The server will attempt to refuse Base64-encoded messages if it notices them. Base64 encoding gums up the list archives and can cause problems for some mail clients. The two biggest offenders on this score are GMail and Microsoft Outlook.
The problem in GMail appears to be related to the outgoing message encoding — one of the settings will encode your message using Base64, rather than Quoted-Printable, even though the options are named “default” and “UTF-8”. Try tinkering with the settings and resending your message.
If you are using Microsoft Outlook with an Exchange server we feel very sorry for you, because someone is forcing you to use one of the worst mail systems ever devised you must contact your server administrator, because you have no control over the encoding used. If you are using Microsoft Outlook without an Exchange server there is something terribly wrong with you you can change the encoding yourself.
Styled Text
The server will reject messages which contain styled text without providing a plain text alternative if it notices them. (Styled text can gum up the list in a number of fiendish ways.) There is an excellent page describing how to turn styled text off in a variety of mail programs at
The lists will reject messages with attachments if it notices them. This is important because some mail clients will add attachments to messages without notifying the user that the message has been modified.

If you are certain that your problem is not one of the above, please contact with an explanation of your problem.