Thunderbird Tools / Message Filters / Filter Rules provides tools to rejecting messages based on content of fields such as from, body, date, priority, To, From and more. However, it does not provide for checking the content of the "Reply To" field. It tried to use the "Custom" feature, but it doesn't seem to allow a space or the special character alt+32 (space) . I've tried using, "Reply contains: babicartsy" and "Reply contains: [email protected]" , but when I run filter, I do not get a match that moves filter to junk. The originators of these particular junk mail messages obviously has access to what should of be a private contact lists, and they do craft very credible messages, but the key that they're junk is in the "Reply To" field which often contains a non-USA location. Suggestions on how to add appropriate filter will be appreciated.