sendmail or dns problem?

From: Rezk Mekhael <rezk_at_clunet.edu>
Date: Tue, 04 Nov 2003 10:34:10 -0800

Hi Manager,

Some users getting this message, from time to time, does any one know
what is it? and what causing it?

binmail: cannot lockf /usr/spool/mail/workord
>>Mail saved in dead.letter
>>554 5.0.0 Service unavailable
>>Reporting-MTA: dns; clunet.edu
>>Arrival-Date: Tue, 4 Nov 2003 10:00:18 -0800 (PST)
>>
>>Final-Recipient: rfc822; workorder_at_clunet.edu
>>X-Actual-Recipient: rfc822; rvommere_at_clunet.edu
>>Action: failed
>>Status: 5.5.0

PS: OS = 5.1
    Sendmail = ESMTP Sendmail 8.12.8
    

--
Sincerely,
Rezk Mekhael
-- 
*** Incoming / Outgoing Mail scanned for known Viruses by CLUnet ***

Received on Tue Nov 04 2003 - 18:35:41 NZDT