In the past I participated occasionally in small to medium-sized (couple of hundred participants) specialized mailing lists, which were very professional. On on

In the past I participated occasionally in small to medium-sized (couple of hundred participants) specialized mailing lists, which were very professional. On one occasion there was a public mailinglist, and after showing some expertice, I was invited to the private one, which was excellent. But all that was more than a decade ago. Perhaps it is still worthwhile not looking for a large community, but for several small specialized ones?