That is oversimplifying, for example what happens when Microsoft seems to make your email to your brother in-law disappear and they tell you they have no control over their spam filters? Or when you sent out birthday invites and every Yahoo user you know presents you with an automated message that your server has been banned forever from sending them mail? So you set out to get SPF records, get DKIM working, get certs... and it doesn't help.
Also, running torrents is different from getting all the DNS set up and forwarding all the ports. And even then, where I live, out of the 10 or so fiber providers I can choose, I know that only 2 allow me to do anything with port 25.
It can be a Pita.