I run several library related professional discussion lists. I have around 100 subscribers at the U.S. Library of Congress. Since a few weeks ago, LC (loc.gov) has been rejecting all of my private mail from [log in to unmask] to my subscribers who have written me about list problems. I cannot even contact the listowner of several lists at loc.gov, even though he thought that he was exempt from all filtering (i.e. blacklist/ whitelist, etc.); he now knows different. He also doesn't know what the problem is, but thinks it is blacklisting (I don't think he runs the email system at LC). Could someone take a look at the error message below and give advice as to what the problem is, and what might need to be done to correct it? I haven't tried [log in to unmask] yet as my experience with "postmaster" addresses is that if the item doesn't bounce (no such address) whatever I send is studiously ignored, never a reply (wasn't like that 15 years ago, but ....). I have this problem only with loc.gov, so far. I can send to anyone at LC from my accounts at the U. at Buffalo, but that's a workaround, I need to be able to send from ccsi.com. Any advice appreciated. Douglas Winship [log in to unmask] ---------- Forwarded message ---------- Date: Thu, 29 Dec 2005 14:43:01 -0600 (CST) From: Mail Delivery Subsystem <MAILER-DAEMON> To: [log in to unmask] Subject: Returned mail: see transcript for details The original message was received at Wed, 28 Dec 2005 14:38:06 -0600 (CST) from infinity.ccsi.com [216.236.168.2] (may be forged) ----- The following addresses had permanent fatal errors ----- <[log in to unmask]> (reason: 451 4.1.8 Domain of sender address [log in to unmask] does not resolve) ----- Transcript of session follows ----- ... while talking to sun8.loc.gov.: >>> DATA <<< 451 4.1.8 Domain of sender address [log in to unmask] does not resolve <[log in to unmask]>... Deferred: 451 4.1.8 Domain of sender address [log in to unmask] does not resolve <<< 503 5.0.0 Need RCPT (recipient) Message could not be delivered for 1 day Message will be deleted from queue