Make your message inviting to your potential readers. DON'T betray confidences. It is all too easy to quote a personal letter in a message to an entire group. If you want to include someone's personal mail in a public message, ask the author for permission first. T send a message to a mailing list that is not relevant to that group.
Some people have to download the messages and pay for the connect time out of their own pockets.
There may be other abbreviations specific to particular mailing lists.