While ethics carries a degree of universality (at least I'd say so), customs are relative. What is okay in one place is an affront otherwise. Respected behavior on one mailing lists will immediately get you off another one.
That's why it's a good idea to

• follow the conversation on a mailing list for some time before posting yourself.

This behavior is called lurking (and, of course, on some lists it is not something other members like to see...).