It is a discussion group for those who are interested in sexual matters and wish to discuss them among similarly interested people. Special measures have been taken to protect the list from spam, and fully anonymous posting is available. Check with your own doctor if you suspect a problem that requires actual medical advice. Sex, and things related to sex. Sex is by definition on-topic.
Related topics are usually on-topic.
Hopefully they don't mutate further. Personal attacks are almost always off topic. The list manager tries to maintain a hands-off policy as much as possible, but if the thread goes on too long, he generally steps in and asks for it to stop. ObSex means an OBligatory SEXual reference. If you just have to post something off-topic, you should include something sexual at the bottom.