Hey just to let you know I host ~300 domains on 1 aws instance. We only have issues when a clients password gets phished, but we also have a limit on the amount of emails per day they can send. So it's never a real issue.

~20,000 emails a day

Going on 4 years. AWS "blocks" are perfectly fine. If you are going to host your own just get your self an Elastic IP and let your account manager know that you intend to send mail. As they (use to? I had to do this 4 years ago) have their own internal anti-spam system which you may hit.

On the contrary I also host my own mail on an instance I have over at [0] which is rock solid and I've had no issues that are not the fault of my own. I would recommend at minimum.

The only thing I can say is if you want to do email yourself possibly use [1] for an easy to setup system and make sure you get a box with minimum 512mB of RAM or around 1GB because ClamAV is fat.

Or go [2] for a hosted solution. Who are doing great things regarding encrypted mail.

[0] https://www.prometeus.net/billing/aff.php?aff=157

[1] http://redmail.com/

[2] https://protonmail.com