We run WordPress as a MultiSite.
The Subscribe by Email tool is sending emails from an email address of a person that isn't remotely affiliated with the site. I can't find anywhere on this specific blog that has any reference to this person (he is not added to the 'users' list, his email address is not the one listed in the Settings, etc.). There is no reason he should be listed as the sender of these emails.
Has anyone reported this recently? I have never seen this before --- but we *did* just upgrade WordPress last Tuesday (related?).