There are two scenarios: the “Email Ignored” and the "No Listings Found". 

The “Email Ignored Timeout” (this is the maximum number of days that an auto-email can be ignored by the client before being disabled by the system), is set to 90 and there are Warnings sent after 55 and 80 days. You should get emails warning you that the auto email is going to be disabled so that you can access it and update/resave it. 

The “No Listings Found” happens for all types of emails, including concierge.  This is where the auto email is prospecting but doesn't find any new matches. The default is 90 in our system. 

 
An auto email that finds nothing for 90 days may never find anything. (This limit exists to prevent searches that never return any results from running indefinitely).