how to make server response to emails

Hi experts, Seen this in many mailing list, but I do not know the logic behind it, hope someone can spare some time to enlighten me. Recall that many mailing list systems all users to send an email with the word "unsubscribe" (or "help" or "subscribe" for that matter.) in the subject line to allow the subscriber to unsubscribe, therefore I believe that there is a way to make the mail server, or which ever it is, to response specifically to text within the mail. Besides using this for mailing list, I think the logic can also be used I other areas such as specific response to Q&A etc. However, I have no idea how this is accomplished and what this system is called, so I need some precious help here. Anyone please? Thanks in advance.. =) Yours faithfully, See Kok Boon Realize Creations http://www.RealizeCreations.com ----------------------------------------------------------------------- looking for jobs? career? chat? look in realPortal