Do they all include the words “postmaster” or “server at”? You also have to handle subscribers who want to unsubscribe. You need a footer with an unsubscribe l

Do they all include the words “postmaster” or “server at”? You also have to handle subscribers who want to unsubscribe. You need a footer with an unsubscribe link and a web server and software at your end that handles that. Or, use a mail list service that handles that.