I use sendgrid to send mail I host on Linode I manage with Cloudron which works with sendgrid and others out of the box. Cloudron is a cool paid server management app but their free tier includes email. Literally give the app your DNS provider details and API key, your sending service details (or internal smtp if you hate it when people actually recieve your email) and the rest is 100% automatic. The free tier limits how many one-button-press apps you can install. They're all regular open source apps, but they nicely maintain docket images for them all and the setup, including DNS for subdomains, is automatic and really smooth. I havr nothing to do with them but I was surprised by how smooth it was.