Product Feedback: Authenticating messaging end users using signed email

Hello, 

This feedback is regarding "Authenticating messaging end users using signed email".

We appreciate the improvement and development of the authentication in Messaging product, however this currently does not benefit us. 

The issue in our use case here is that we have several Zendesk instances where we have multi brand and in each of these brands we allow customers to register the same e-mail address. In this case, e-mail address for the end-user is the same but external ID is always different which causes issues with authentication. 

What we need is a solution where we can use only user email address for authentication, to make sure that authentication behavior will be same as in Zendesk chat and only user email address will be passed to Zendesk upon authentication.

I have already noted this in a previous feedback post here.