Huh? I'm not even sure how you came to that conclusion. Gmail is probably tougher on mail servers using IP6 addresses because they're plentiful and I suspect s

Huh? I'm not even sure how you came to that conclusion. Gmail is probably tougher on mail servers using IP6 addresses because they're plentiful and I suspect spammers were having a field day setting up temporary mail relays forcing google to play whack-a-mole. I used to run my own email server years ago but spam and spam protection measures have made it time consuming and annoying. I'll leave it to the professionals.