>they require you to transfer your domain to GoDaddy

Not according to this page:

https://support.microsoft.com/en-us/office/use-your-own-doma...

But isn't that product ("Outlook Premium") closed off to new subscribers since 2017? (https://support.microsoft.com/en-us/office/outlook-com-premi... ) I also had a similar experience to the parent poster, i.e. MS support required transferring the domain to godaddy before one could use it for Outlook if using a consumer-focused O365 plan.

Oh. Color me corrected. That requirement honestly sounds insane.

I've been on Mailbox.org for a while now while co-evaluating others. Apart from a few UI quirks and slow-ish support, the service has been rock solid and nice. It also supports push email for ios devices.