>I added someone with a @midway.uchicago.edu address to my list a few
>weeks ago.  For the next ten days, I got "Service unavailable"
>messages, so I deleted him.
>
>I simply cannot contact him and have NO reason why.
>
>Any takers?
 
Sure!  You have a reason, but it's buried in the error messages.
 
>   ----- Transcript of session follows -----
>mail: /var/spool/mail/dswilson: cannot append
>mail: cannot open dead.letter
>554 <[log in to unmask]>... Service unavailable
 
The "cannot append" message is the key.  On Unix systems, this message
can indicate several different things:
 
        1 his personal mailbox (/var/spool/mail/dswilson) has become
          so large that new mail cannot be added.  This problem is
          usually found on System V Unix and its variants.
 
        2 the mail directory/partition (probably /var, although some
          sites use separate disk partitions for /var/spool/mail) is
          full, so no one on that system is getting mail.  This one
          can happen to any Unix system.
 
        3 dswilson has, for whatever reason, changed the access permissions
          on his mailbox in such a manner that the mail program no longer
          has write access to it.
 
There are a few other possibilities, but they are rather obscure; I'll bet
on one of the three scenarios listed above.
 
You may wish to drop a line to [log in to unmask]; if that
message is delivered successfully, you can eliminate scenario 2 from the
list above.  The postmaster should be able to fill you in on the details.
 
[log in to unmask] needs to be educated in the importance of
*routinely* reading/clearing one's mailbox when subscribed to heavy-
traffic lists.  8)
 
--Wes