[jeroenhd]

You can self host if you make sure to monitor for signs of hardware failure and ensure that replacement hardware + good backup strategies are always ready if you rely on it for hosting services for customers/other people.

If it's just for you and you have the hour or so per week to dedicate to updates and maintenance, then I don't see why not. I run two servers in my room and they've worked fine with minimal maintenance so far, except for a few old hard drives that needed replacing and a fan that I couldn't get replaced because of a screw I stripped years ago.

There are quite decent cloud machines out there if you just look beyond the big guys like AWS and GCloud. https://contabo.com/en/vps/ has decent servers for cheap, as does https://www.hetzner.com/cloud

If your emailer service makes direct contact with destination SMTP servers, then running from home is probably not an option. If you use an external SMTP server to deliver mail to the destination servers then this won't be a problem.