A listserv user gets the 'monitoring' status when emails sent by the listserv system are bounced back. After a certain number of bounced emails within a certain timeframe, the user will automatically be removed from the list - the system assumes the email is no longer in service. If the user wishes to be on the list, they will resubscribe.

On our system, if the owner has been adding emails to the list manually, the emails might not match the 'canonical' email address used and will be considered the wrong email address and bounced.