Hello,

I finally resolved why GMail will accept mail from 3 domains and not the 4th. GMail does not appear to accept email from DYNU SMTP6 (72.51.58.75). I get an error message with that IP.

The other 3 domains work well with the other servers such as DYNU SMTP2 (162.216.242.35).

The SMTP server used in long form is "triadofrevenge-com-smtp.dynu.com" which is routed to SMTP6.

Any help with resolving this is appreciated. I have spent several days fooling with SPF, DMARC, DKIM, and more. They were not the problem (never dreamed SMTP6 would be rejected with an unacceptable IP by GMail).

Thanks,
Thomas