I asked the list about this and then wrote to the postmaster of att.com...
here is his reply:
 
Date: Tue, 4 Aug 92 10:49 EDT
From: [log in to unmask]
Subject: Re: Delivery error notice sent to list IPCT-L
 
	I've been looking into this recently ... I think I have it
	narrowed down. It appears that ATTMAIL's mailer won't
	accept email that has *any* header line longer than
	like 128 chars !!
 
	Example:
> From: internet!pucc.Princeton.EDU!GUVM.BITNET!IPCT-L
> 	internet!pucc.Princeton.EDU!nevada2.BITNET!msmauri (Interpersonal Compu
>        ***ting and
 
	I've been in conversation with them to 1) confirm that their software
	does this and 2) stop it.
 
	We here at att.com do gatewaying for attmail.com. I am pretty sure
	that whomever you send the list to either forwards their email to
	attmail.com from their att.com address or you have an attmail.com
	address in your list.
 
 
	Joseph Judge		[log in to unmask]
 
  }|{ mauri
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