One of our users is facing a login issue on our platform. We've noticed they have two different emails e.g. one is an email attribute

<mailto:johnl@example.com|johnl@example.com>

and their loginId is

<mailto:jonathan.lee@otherdomain.com|jonathan.lee@otherdomain.com>-t2....

Would the user have to use

<mailto:jonathan.lee@otherdomain.com|jonathan.lee@otherdomain.com>

to login since that's what is their login ID is tied to?

To login with SSO you should use the SSO domain.