SMTP is among the things I wouldn't self host. Chances are your entire ISP is already blacklisted for some reason and mail ports are blocked. You'd have to create a relay host on some cloud provider and secure it to avoid having an open relay then navigate through all the configurations related to spam and malware filtering, gray lists, DNS registers and so on.

Dealing with mail servers is the only thing I don't miss from my classic sysadmin days. Although it should be noted popular MTA software nowadays are really solid software.