[kazinator]

> Is there something else we should be doing?

Trying different SMTP providers, probably.

Your mail domain is something that appears in the From: header of your e-mails.

However, mails can be rejected as spam even without any of the headers or body of the e-mail being seen, at the SMTP level, and that could have to do with who you route your mail through, or who your sending or forwarding mail servers are co-located with in the same IP block. IP addresses which have nothing to do with each other can tarnish each other's e-mail sending "reputation".