Potential challenges if we choose to implement this:
How do we decide which domains are worth including and what value to ascribe to them? As an example _@adobe.com is a likely signal that _ works for Adobe, but @gmail.com carries no such value.
E-mail addresses are trivially easy to create and potentially use for fraudulent purposes.
Per discussion in 21 October 2024 CAWG meeting, we may want to offer verified e-mail address as a sign of affiliation.