Hello All! My first post and it's a doozie. Any help would be great!Some version information:Client Email Program: Outlook 2003 11.6568.6568 (SP2)Client OS: Windows XP Professional SP2Server Email Server: Exchange 2003 6.5.7638.1Server OS: Windows 2003 Server 5.2 R2 (Build 3790.srv93_sp1_rtm.050324-1447 : Service Pack 1)My issue is with sending emails from our Microsoft Exchange Server to certain domains. Almost all emails work but to these particular domains, the emails are not received by the recipient and after the retry period has finished, we receive Non-Delivery Reports that state the following:recipient@receiver.com on 05/03/2007 2:09 PMThis message was rejected due to the current administrative policy by the destination server. Please retry at a later time. If that fails, contact your system administrator.<mail.sender.com #4.3.2>With some of the domains who didn't receive this email, we found that the issue was that their firewalls had blacklisted us. After speaking to their administrators, we were able to fix this issues and emails were received.However, with the remaining domains, this was not an issue. We checked both firewall and antivirus configurations and found no such blacklisting regarding our domain.We then checked our DNS settings due to the fact that some ISP's now perform a reverse checkup on the mail domain. With our ISP, we made modifications to the DNS to adjust the PTR record to point to our mail server:PTR Name: mail.sender.comPTR Address: 1.2.3.4These changes to the DNS did not work.At this point, we tested via telnet (i.e. telnet receiver.com 25) and performed a test email send through telnet. We verified that these emails were received and now know that this is not a connection issue with their servers.After verifiying that telnet emails worked, we installed Microsoft Network Monitor 3.0 to see if we could find the issue through the data packets transmitted by Exchange.The issue lies here:On emails that fail, when communicating with the email server through SMTP, failures are guaranteed if we receive this SMTP response after their SMTP server requests DATA (contents after receiving who the email is sent to and who the email is sent from):Rsp 354 End data with <CR><LF>.<CR><LF>, 37 bytesAfter receiving this response, we see that our Data payload is sent but we immediately receive the same response (Rsp 354) from the receiving server. Our sending server then begins to send more Data payloads over and over until it times out and fails with the following SMTP response:Rsp 421 Error: timeout exceeded, 29 bytesNow, examining the Data payloads gave us our first indication of what the problem was. We found that our emails were not conforming with the receiving servers format of <CR><LF>.<CR><LF> and that the end of the emails were not ending with a "." to indicate that the email was complete. Upon further tests we found that Microsoft Exchange was encoding the email without the "." at the end and rather putting "=20" as a carriage return and the repeated Data payloads (the ones sent after the second Rsp 354) are identical and do not end with a "."After finding out that this was the issue, we sent a plain text email through Outlook. The email was received automatically. This leads us to believe that this is an encoding issue with either our Outlook or Exchange system.These are the current settings that we have changed to in both Outlook and Exchange. None of them have fixed the problem:Outlook:Tools > Options > Mail Format > Internet Format- Set Outlook Rich Text Options to: Convert to Plain Text FormatTools > Options > Mail Format > Internet Format- Set Preferred Encoding for Outgoing messages to: US-ASCIIExchange:Global Settings > International Message Format > Properties- Changed Message Format for character sets to: US-ASCII for MIME and non-MIME- In advanced, changed Exchange RTF to never useDefault Virtual SMTP- Changed FQDN to be mail.sender.comIf anyone has any information that can help me out with this, it would be great. I can post the information found in the Network Monitor for failures and successes (so that you can compare). We've looked at this for days now and we hopefully a new set of eyes can see what we've been missing.Thanks in advance!Chris Lorico

Chris,Any luck figuring this out? We're running into the exact same problem.Jacques

I dont want to leave a weak post, but i noticed your version of exchange didnt have any service packs. are you up to date with exchange 2003 sp2? http://technet.microsoft.com/en-us/exchange/bb288486.aspx

Yes, we have updated to Exchange 2003 SP2.

Yes the problem is now solved. We had to change the MTU pack size in the router to be 1492. We found this out after speaking with Microsoft Techncial Support.

Thanks. We're about to give that a shot. Do you remember what the reasoning was on the change? It seems like a bit of an odd one. Did it have to do with using a DSL link or anything like that?

Not too sure about the reasoning. When we did our testing,pinging at a higher MTU size resulted in no replies. So we set the MTU size in the routeras well asthe NIC on the exchange server to thesame value. I forgot to let you know that we made that change on the NIC of the exchange server. That required changes in the registry so you might need to research your NIC to see how that can be changed. Hope that helps.