In addition to Pete Weiss' observation that you have set a 16 day delay on
automatic deletions, I will suggest that those singleton items, for no
subscribed address, are listname-request, or "you are not allowed to post
or "your posting has been forwarded to the moderator" type errors.  That is
someone, who is not subscribed, sends something to the list or to
listname-request, which generates an auto-reponse. The auto-response cannot
be delivered so you get an error message.  Not infrequently these are spam
items.  I get a lot of these every day of the week.

Douglas Winship  [log in to unmask]