I did almost exactly what you describe and it works flawlessly, but I only send a small volume of mail (my own). Digital ocean droplet $10 a month, but it would run on a $5 one if you don't also have caldav/sftp/kerberos/vpn/etc there like me.
Fun Fact: Microsoft Exchange has no native support for DKIM and tons of business run that in house, often on 'business class' connections without correct reverse IP records.
I don't know whether OP uses a home connection, but that makes a big difference. It has some pros and cons:
A VPS (with its dedicated IP address):
- Usually has a good reputation, though you might have bad luck. Switch early on when you notice this. Doing it later just nullifies any trouble you had building its reputation.
- Is hosted somewhere in the cloud. (I used to hate the term "the cloud" but it's actually pretty apt and funny if you start seeing it as "they have no idea where their shit is and who has access to it, both physically and network traffic".)
Hosting at home:
- Might be trouble with your ISP if you don't live in a country with net neutrality and port 25 is closed.
- Gets you a lower reputation score by default, so it takes slightly longer to build.
There is also a third option, set up a OpenVPN server and connect the home hosted SMTP server to the internet though it, gives you the best of both worlds I figure.
That might actually be a good idea! I wonder whether a hosting provider or ISP is more reliable in not snooping SMTP traffic, but assuming that is equal, it sounds like the best of both worlds indeed.
Fun Fact: Microsoft Exchange has no native support for DKIM and tons of business run that in house, often on 'business class' connections without correct reverse IP records.