I also host my own email. In my case, Google always routes the first email I send to a new Gmail address as spam. After the recipient marks the email as good, future emails are received as expected. The only way around this is to advise the recipient via Gmail that I've set an email to them via a different route, so that they can check their spam and mark the email as good. This has been going on for at least two years.

Basically, Google are shadow-banning me till they get caught. I think this should be illegal.