I think something he just plain doesn't get... who on earth is the target demographic. There's no shortage of e-mail services, outlook, yahoo, gmail, as public easy to use ones.
So what I gather, the closest to a major "feature", is to remove formatting and image ability from the e-mail. Which... most likely means existing e-mails formatted for other platforms, will error out or be unreadable unless individuals choose not to use their formatting ability from their mail clients?
Gmail rose to fame, because it actually solved a real problem. IE at the time gmail came out, hotmail was offering like 10 MB of storage. Google offered 1GB. A change so big people thought the anouncement was just an april fools joke (admitted, announcing it on april 1st was probably intentional for that as well).
I guess, but even there... I fail to see the target there. IE truth social and xitter at least have a reason alt right extremists need them... IE facebook and old twitter would occasionally ban people or put fact checks on some nazi rhetoric and blatent false stories. To my knowledge no e-mail provider is going to ban you for sending that FW:FW:FW:FW: My dog was infected by my son's friends covid vaccine, and my hatian neighbor became trans after eating it.