Malformed outgoing email address?

I’m seeing sporadic email bounces that I can find no pattern in. Below is
an example. Has anyone seen this kind of problem before and have ideas
about th cause? All email addrs in the requestor/cc/admincc are valid
(and, in this case, very simple).

AlchemyRT is the queue
tank.intrinsic.com is the machine
rt.intrinsic.com is an alias to tank

The original message was received at Wed, 14 Nov 2001 16:07:25 -0800
from nobody@localhost

----- The following addresses had permanent fatal errors -----
‘AdminCc of AlchemyRT Ticket #159’:;

----- Transcript of session follows -----
501 5.1.3 ‘AdminCc of AlchemyRT Ticket #159’:;… List:;
syntax illegal for recipient addresses

[-- Attachment #2: ATT00052.dat --]
[-- Type: message/delivery-status, Encoding: 7bit, Size: 0.3K --]

Reporting-MTA: dns; tank.intrinsic.com
Arrival-Date: Wed, 14 Nov 2001 16:07:25 -0800

Final-Recipient: RFC822; "501 List:; syntax illegal for recipient addresses"@tank.intrinsic.com
Action: failed
Status: 5.1.3
Last-Attempt-Date: Wed, 14 Nov 2001 16:07:25 -0800

[-- Attachment #3: ATT00055.txt --]
[-- Type: text/rfc822-headers, Encoding: 7bit, Size: 0.8K --]

Return-Path:
Received: (from nobody@localhost)
by tank.intrinsic.com (8.11.2/8.11.2) id fAF07PN20428;
Wed, 14 Nov 2001 16:07:25 -0800
Message-Id: rt-159-1418.1.58234749980672@AlchemyRT
RT-Ticket: AlchemyRT #159
X-Mailer: Perl5 Mail::Internet v1.40
RT-Originator: rdy@intrinsic.com
Content-Disposition: inline
Content-Type: text/plain
In-Reply-To: rt-159@AlchemyRT
Managed-BY: Request Tracker 2.0.7 (http://www.fsck.com/projects/rt/)
Precedence: bulk
MIME-Version: 1.0
Content-Transfer-Encoding: binary
Sender: Nobody nobody@tank.intrinsic.com
Brian McClendon bam@intrinsic.com 650-966-6804

Brian McClendon wrote:

501 5.1.3 ‘AdminCc of AlchemyRT Ticket #159’:;… List:;
syntax illegal for recipient addresses

You are using Sendmail[tm] brand sendmail and have not
followed the instructions regarding UseFriendlyToLine
in config.pm, at a guess.