Problem with Sendmail on a Stardent GS-2000

[Gerson H Cohen]

I cannot receive network mail on our Stardent GS-2000 system.  I can
originate such mail and is is delivered properly.  Incomming mail was
clearly being received (as noted by logs on the sending machines and
as inferred from syslog on the Stardent), but was giving the status
"Service not available".  Sendmail then tries to reply to the
originating machine and cannot get the message out, failing with the
same error.  I have twiddled somewhat with sendmail.cf and the status
has now changed to "Host unknown".  Here is part of syslog, showing a
successful outgoing message and the failure mode I discribed (I have
stripped the time stamps and hostname [molstr] to shorten the lines, I
have also split the two lines indicating the error status):

sendmail[1036]: AA01036: message-id=<9010091616.AA01036 at molstr.niddk.nih.gov>
sendmail[1036]: AA01036: from=ghc, size=26, class=0
sendmail[1038]: AA01036: to=ghc at vger, delay=00:00:02, stat=Sent
sendmail[1040]: AA01040: message-id=<901009121855.20200167 at VGER.NIDDK.NIH.GOV>
sendmail[1040]: AA01040: from=<GHC at VGER.NIDDK.NIH.GOV>, size=247, class=0
sendmail[1042]: AA01040: to=<ghc at molstr.niddk.nih.gov>, delay=00:00:00,
 stat=Host unknown
sendmail[1042]: AA01042: message-id=<9010091616.AA01042 at molstr.niddk.nih.gov>
sendmail[1042]: AA01042: from=MAILER-DAEMON, size=0, class=0
sendmail[1044]: AA01042: to=<GHC at VGER.NIDDK.NIH.GOV>, delay=00:00:00,
 stat=Host unknown

Please try to help me out of this.  If you are willing to examine my
sendmail.cf, I will provide it.  Please reply directly to me
(GHC at NIHKLMB or ghc at vger.niddk.nih.gov) because I do not subscribe to
info-unix and will miss your advice.

Thanks for any help or hints,

Gerson Cohen, NIH
301-496-4295