What is pipermail?

When you have a doubt, the first thing to do is to use a search engine. If you search well and are unable to find anything relevant or pointers to further information, then ask. This is better for you because you may answer your inquiry faster, and better for the rest because you don't consume volunteer's time which is better spent in other tasks.

Internet 101: When in doubt, do a !w pipermail, or search Wikipedia.
!w pipermail gave me: https://en.wikipedia.org/wiki/GNU_Mailman