I'm not sure if that is a correct approach as it's not true for every user. Plenty of users are not using @fedoraproject.org mail for Bugzilla at all.

Yes but if they have set both nothing changes. If the user changes only email in FAS after they have BZ account created with @fedoraproject email, the issue linked happens. I think this is a recurring thing.

Let's give this a try, you are right that it prevents issues when people change their mail on FAS side and forgot to do it on Bugzilla. They still have the rhbz mail field if the mail doesn't correspond.

The one wrinkle on this is that the user has to be a fedora contributor (ie, in at least one non cla group) to have a fedoraproject.org alias.

In this context it should be ok because we also check for packager I think? but we should make sure there's not some broken part here...