I believe that most of the mailing lists are now quiet and the conversation has moved to Facebook. There are many wonderful PWS support groups on Facebook. The community is welcoming and helpful and inclusive. Just search for Prader-Willi Syndrome on Facebook and you will find many options. Most of the items on this site are more likely to be discussed on a Facebook group called "Living Well with Prader-Willi Syndrome." It is a closed group and you have to be approved to join. What this means is that if the Living Well group represents your entry into the PWS Facebook world, you will get a message confirming that you have a connection to PWS and are not just interested in selling things to our community.
Old listserves (for history's sake!):
Prader-Willi at Yahoo Groups is a general purpose mailing list. The archives are publically available.
PWSA-USA-0-5yr at Yahoo Groups is targeted for parents of younger children. Moderators need to approve new members, who can then post and view the archives.
Asociación Madrileńa para el Síndrome de Prader-Willi Forum at the Madrid PW Assn. General Forum in Spanish. No registration needed.
PositivelyPWS Yahoo mail group. Said to discuss alternative ideas/therapies/treatments....