Many years ago, seeing the client IP in email headers was the norm. Now, privacy as well as legal obligations are more common. Gmail, Outlook et all, all hide the sending IP, for good reason.
I think there should either be an option to remove the IP or obfuscate it (replace in the headers with a sending ID X- header. Of course, we still have logging so we can find out who it was.
Blacklists don't generally list the sender of the message but the server sending the message so that won't change.
I feel this should only apply to authenticated sending of messages (same applies to webmail).
Whilst there is the argument of abuse (spammers) vs privacy. I feel privacy trumps anything else as well as doing right by what are paid customers. We can still find out or identify spammers either way.
