In our Jenkins, we have a user named "jenkins"
We have jobs that use the mailer plugin to send emails.
On those jobs, if we select "Send separate e-mails to individuals who broke the build", we notice that intermittently, builds on those jobs will attempt to send emails to the email address for that "jenkins" user, even though that user is not configured to receive emails in the job configuration. I have seen this on builds that fail and that succeed.
It's almost as if the detection for "who broke the build" is identifying the jenkins user as a culprit and deciding to send that user email. I can find no evidence, though, that the jenkins user is responsible for breaking these builds.