Email as alternate login ID Breaks Admin / Privileged Accounts

We have a tenant with the "email as alternate login ID" enabled so users can log in with the email address and not think about their UPN.

Unfortunately, this breaks privileged accounts that don't have a mailbox enabled but still need to receive email to that admin SMTP address.

Historically, you simply add that proxy address to your regular account and there isn't a problem. But with the email login enabled, there is now a proxy conflict because Entra reads that admin proxy address as the login for the regular account.

I know within entra you can configure some plus addressing but for external entities with SSO configured and using your privileged account, that doesn't work.

Any thoughts?