I've used https://mailu.io. It works well, but your biggest problem is going to be getting over the spam filter hurdles of the email giants of the world. Even if everything is properly configured (including dkim / spf / whatever else they've added) your messages will get plopped in the spam folder.
My experience is, that the „quality“ of the mail server‘s IP really matters. The worst experience I got was with digital ocean. A lot of providers just don’t accept email from their IP ranges. Some of them just completely block all DO IPs on router level, and refuse unblocking.
For my current server I had to switch IPs a few times, until I got one that was not blocked by any of the major providers. Unblocking a once blacklisted IP seems to be practically impossible.
And hotmail or outlook.com just mark a lot of email as spam. I see it now as a problem of the recipients. Office365 just accepts the same emails, it seems to be a strategy of the free mail providers, to give their non-paying customers a worse experience.
We got a /24 at our data center and the reputation was, unfortunately, poor. I went through all of the public reputation lists and asked to be removed. It took about three months of incremental effort, but the reputation for the entire /24 is clean now.
This is with a "real" mail server, and not mailu.io, but the idea is the same.
I just went to my cloud provider of my choosing and started to add floating IPs. After a few tries I got a good one. I went through the unblocking process once, and I decided not to do it again. Especially Microsoft gave me a hard time, they started to request documents and then let me wait a few weeks until they replied: we don’t unblock, and we don’t tell you why.
Is it possible that Microsoft distrusts your IP range? Some providers are known not to be very responsive to abuse reports. And then whole IP ranges get (soft) blacklisted, and individual IPs can’t be unblocked, without having a very strong case.
