Your ISP probably offers the most basic mail setup you can build with the lowest effort. Your ISP as no reason to give a world class mail service because that's

Your ISP probably offers the most basic mail setup you can build with the lowest effort. Your ISP as no reason to give a world class mail service because that's not something they're good at or that they could make money from. It's just one something they think is expected nowadays. I don't think this is wise advice from a privacy point of view, considering your ISP knows all your internet habits including all your connections to any service you'll ever use and that most ISPs don't have your interests in mind.