As the buildbot sheriff, I am in the extraRecipients list for all of my MailNotifiers?. Because of this, I usually can't tell if I'm being sent the "build failed" email b/c *I* broke the build or just because I'm on the extra recipients list. Thus, I have to manually check which is usually a waste of time. It'd be great if the extra recipients list was CC'ed instead of being on the TO: list. The notifier does appear to merge my name if I was at fault (i.e. it's only in the TO: list once) so this does require some extra smarts if I was actually to blame.
I took a look at the code in the MailNotifier? class but I don't understand Deferreds so I wasn't quite sure how to do the change. I could also see a case where not everybody would want to use the CC: list so some extra option might be needed.