Over the past weekend I had occasion to relate the OPs story to TWO airline managers. Unanimously they exploded with "He'd be fired on the spot, no ifs ands or buts, for an infraction of company policy re:confidentialty issues."
If you'll recall, I didn't suggest the OP should contact UA with identification of the FA who e-mailed him.
If you'll recall I urged the OP to make it clear to UA that confidentiality had been breached on a recent domestic flight and that the OP would not participate in any further such until confidentialty could be guaranteed.
I call that "kicking in the right direction"--everyone benefits.
And maybe UA makes it $#%& clear to employees that they have a particular obligation with regard to manifests and surveys, etc., that reveal pax ID info.