mozmail.com domain rejected by Github

[fatalerrors80]

When adding an address in Github profile, this error appears:
Error adding xxxxx@mozmail.com: Email domain could not be verified.

┆Issue is synchronized with this Jira Task

[CodingMarkus]

I use a so called custom address at GitHub and at Apple. Could it be that this really only affects random addresses?

Paying users can choose between those two address types. Random is xxxxx@mozmail.com with xxxxx being random digits and letters. Custom is <whatever>@<subdom>.mozmail.com, and you chose <subdom> when you sign up for a paid account and you can choose <whatever> yourself to be whatever you want it to be.