Some old WMFers continue to receive e-mail from being subscribed to things. However this e-mail is bouncing since their WMF e-mail has (rightly) been turned off. Outgoing staff should probably swap their e-mails to a personal one :)
Also sometimes people setup weird e-mails that just don't work.
Due to the way Phab's MTA jobs behave, they continue to bounce again and again and pile up the daemon queue. Silly Phab.
Former staff are always welcome back as volunteers, and if these people want to regain their accounts I'm more than happy to restore it at that point if we can sort out the e-mail issue.