Firebase Auth and Email aliases

[yoni...@gmail.com]

I've seen some cases where the users insert their emails using their IdP, but the email that is seen in Firebase Auth is different - could be a different domain or even the name itself.

I assume this involves some kind of aliases, email forwarding or something similar.

The question is - how can I really know this is the user I had expected?

I would like users to invite other users by their email address, but this kinda makes it impossible as I would like to check the claims of the user to make sure this is the expected email and that it's verified.

Is there any way to get the email that was originally used during the sign-in? Or is there another way to safely link all this data together?