One thing worth noting if you consider running any mail server yourself - is checking the IP address / range that your VPS provides you. I've had outbound email blocked or blacklisted with IPs from DigitalOcean - especially on Yahoo, whereas Linode or AWS give you better reputation.

It was virtually impossible to get unlisted on Yahoo for IPs that are owned by the hosting provider, and I'm not sure all providers would make the effort of doing this on your behalf.

I suspect lower-end VPS providers are even worst in that respect.