Email.

As someone who has been self hosting some stuff and generally aspires to work in IT, it is simply unfeasible to expect services like this for free

Would it cost me less to host such a server divided by x users? Yes

Do I have x users I can sustainably service without burning out? No.

So its either a managed server for like 15€ per month + a bunch of work or a paid email provider, in my case fastmail.