It's not that simple with mail. Most centralized mail servers have strict requirements for domains that they will not sort into spam, and if you are sending a lot of mail from your personal server, you will probably end up on a spam list. I don't do it, so I am not an expert, but hosting your own email server to do anything useful is pretty complicated.

Still, I guess you could argue that this is as it should be, as it prevents people from making spam servers, while still theoretically not being impacted that much for personal use servers. But I don't personally know anyone who seriously hosts their own email server anymore.