Quick summary

When a domain expires, email accounts @thatdomain will stop working.

This is problematic because users will stop receiving notifications or perform an account recovery.

Users should be discouraged from using an email account that's linked to a custom domain they also have registered with us.

Case and point: sq0UY-cat-p2

Steps to reproduce

1. Sign up for an account using a free (e. g. gmail) account
2. Register a custom domain and add professional email using that newly registered domain
3. Update your account email at /me and replace the original gmail email with the newly created custom domain email
4. Let the domain expire
5. You're stuck

What you expected to happen

We should programmatically detect if they email a user is trying to add matches a domain they have registered with us (or pointed to us, for that matter). If we detect they are trying to do this, we should show a message discouraging them from making this change.

What actually happened

We let users make this change and get them in a potentially tight spot.

Impact

All

Available workarounds?

Yes, difficult to implement

If the above answer is "Yes...", outline the workaround.

There are secondary account recovery methods but they take time and effort.

Platform (Simple and/or Atomic)

Simple, Atomic

Logs or notes

No response