If you don't own that domain that your email goes to, you don't own the email address.

Any number of things could happen to cause you to lose access to that email address:

- the company who owns that domain is sold - the domain is sold during bankruptcy proceedings after the company goes under - the company that owns that domain decided to get out of the email business - the company has a vested interest in migrating you to a new domain (as is here)

I'm surprised at the number of people – even in tech - who are willing to use an email account on a domain they don't have any control over.