Mail: YAST_ASK in "From:" line

Hi! I'm running SuSE-6.3 over kernel version 2.4.1. When sending a test message to my own address, using "Pine" or "Mutt", the "From:" line in the message received reads "robin@YAST_ASK", rather than "...@cosby.demon.co.uk", even though this user domain is configured in both programs. I'll be grateful for any information about why this happens and how I can ensure that all messages sent show my correct address in the "From:" line. TIA -- Robin Cosby