It looks as though the mail service won't support custom domains.

reifnir · on May 1, 2019

Got a reply from my question asking about custom domains: Hello,

On Tuesday, 30 April 2019 at 23:29, [me] wrote: > Hi there, will you support custom email domains? I'd love to migrate from > Google Apps!

We're looking into it, but cannot say nothing for sure for now.

> -[me]

Kind regards,

-- [support person] Purism support