problems installing mail package

[SINMICD at YaleVM.YCC.Yale.Edu]

I am having problems setting up my Iris 4D to receive
mail from other sites.  I have been able to successfully
send mail out from the Iris to other machines, but when
I try to send mail back, this is the error message I get:
 
============================================================
 
From: MAILER-DAEMON at friedel (Mail Delivery Subsystem)
Subject: Returned mail: unknown mailer error 5
To: <sintchak at csbvex>
Status: RO
 
   ----- Transcript of session follows -----
mail: Options MUST PRECEDE persons
554 <oxalis at friedel>... unknown mailer error 5
 
============================================================
 
Any ideas on what I might be doing wrong?  I have tried both
the sendmail.cf that came with the Iris and also the Harvard
sendmail.cf package -- I can get both to send mail out, but
incoming mail always gets sent back with the above message.
Thanks in advance for any helpful suggestions.
 
Mike Sintchak.
sintchak%hhvms8 at venus.ycc.yale.edu