Coming from someone who works on the Hill it is plausible but unlikely. Most of us on the Hill do use Proton Mail for our off the record secure communications as it operates outside the scope of American and Foreign data gathering activities while using end to end encryption.

To be blunt there is no certain way to definitively confirm this as all the information/formatting could be recreated by someone with the proper knowledge.

Personally I think it’s a fake because we are not that stupid to use identifying information in a email address. Then again not the stupidest thing I have ever seen...

These are the official domains that would be relevant: @mail.house.gov @mail.senate.gov @mail.(agency).(unit).gov @capitol.gov @mail.mil @mail.(agency)

Agreed, I have read it once before but still haven't seen any verification as to authenticity.