not sure I follow, the mail handling is set at domain DNS level - one may choose to handle their custom domain with another provider at any time it is zero lo

not sure I follow, the mail handling is set at domain DNS level - one may choose to handle their custom domain with another provider at any time it is zero lock-in, I can read my custom domain email with them with minimal fuss, or I could handle it myself in any other manner if I choose so.