auto-expire:
    
   When an article is read (the word `read' here being a verb, not a noun
   referring to the mark), Gnus also marks it as expirable (`E'). When
   the expiry process occurs, it explicitly uses the articles marked with
   `E' as the set of articles eligible for expiration.
   
    total-expire:
    
   No `E' marks are used or relevant at all. When the expiry process
   occurs, articles marked as read are eligible for expiration. Note that
   this means articles that are not unmarked and are not marked with
   either `!' or `?' as both of those marks are just special ways of
   saying "unread".
   
    The real difference:
    
   The benefit of auto-expire is that in really huge groups (several
   thousand messages) or groups with really old ticked of dormant
   messages, the expiry process will be much faster. This is due to the
   fact that Gnus has an explicit list of eligible articles, instead of
   having to rebuild such a list each time expiry is invoked.
   
   The benefit of total-expire is that it is simpler. There is no such
   thing as a special mark for expirable messages. All articles that are
   read and not marked otherwise will be expired once they are old
   enough.
   
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   This FAQ is Copyright © 1995, 1996 Free Software Foundation. Please
   send comments, and suggestions to Justin Sheehy
   <URL:mailto:dworkin@ccs.neu.edu>.