[StayTrue]

I had this problem for years. I would get the block lifted and it would return in short order. I surmise it’s because my mail server runs on a VPS and other users on my subnet are not well behaved (actually I know this for a fact).

I solved the problem by paying for a next hop SMTPS server as an upstream smarthost for non-local mails. That means my mails come from a subnet that fronts TONS of other servers/domains. That makes it a bigger headache for MS to block.

Sad but there you go. I do not use the external service for inbound. Inbound mails come direct to my server per the MX.

[deltarholamda]

I do the same thing, also with mailgun. It's generally much easier to deal with, especially if you have a fairly low volume of outgoing emails.

Mailgun has been very good to me, highly recommended.

[jbotz]

Who do you use for the upstream smarthost?

[StayTrue]

mailgun.com