How can I know when a subscriber has posted their first message to the list?
The most effective thing you can do to grow your list, is to thank and welcome people that have just overcome their fears, and posted a message to your list.
Just a simple private email directly to them, from you, the list owner.
Turning on this option will tell our system to track when anybody posts for the first time. And forward you a copy of their message. The Subject line will indicate that it's their first post.