I've been using a docker mail server[0] pre-configured for years without issues. I switched from DigitalOcean to Vultr and finally landed on Hetzner. Always had no issues delivering or receiving messages from/to the big guys.
I'm also addicted to watchtower[1] to keep it automatically updated without hassle.
[0] https://github.com/tomav/docker-mailserver [1] https://github.com/containrrr/watchtower