We used to have users' email addresses looked up in Perforce, but it has stopped
working. I think this happened in the 1.0.15 release of the plugin.
I found issue 1374 which was a request to implement this lookup in the first
place, and stumbled upon issue 1022 where the submitter mentions a change to
PerforceMailResolver in October (fits with 1.0.15).
Symptom: Mail is sent to "username" instead of "email address" (for users not
already registered in Hudson's list of people).