Earlier quoted context omitted.
You can perfectly "host your own email server" while sending outgoing mail through a smart host. No falsely-tagged-spam issue that way.
No, in my experience, selectodude is right. I've written this rant before but I think it's worth sharing repeatedly, so here goes again: The big players (Google, in particular...in case it's not clear, the bulk of this rant is leveled at Google; Microsoft is an offender on perhaps 25% of the level, Yahoo just doesn't seem to care) have ZERO interest in "playing nice" with small e-mail servers. My experience running m…
This was your actual problem. The large providers (gmail, outlook, yahoo) and appliance vendors (ironport, etc.) are all now treating "unknown" senders as spammers. If you don't send a large enough volume of emails, you will never make it into their reputation tracking lists because "it's not worth it". End result, you are considered unknown and will be treated as a spammer forever.
It is a huge organically grown cartel where the protocols work but you cannot enter a small player, no matter how well you behave. It is a shame, but there's nothing you can do about it :(