I have an Exchange 2003 SP2 server running on Win2K3 SP2. I'm having trouble sending mails with attachments to yahoo and hotmail addresses. The mails get stuck in the exchange mail queue and blocks any other emails to yahoo and hotmail. If i sent mails to yahoo and hotmail without attachments, they go through fine. I have more trouble delivering to yahoo users than hotmail. I did the same test (with attachment) to gmail and the mail went through fine. I'm using a 3MB attachment with default attachment settings for the testing. Sometimes a force connection or reboot would fix the issue but it would act up again when attachments are sent. This used to worked fine until a few months ago. I checked my IP to see if it's blacklisted, it's not, no open relay, and reverse DNS is set up and working correctly. Any help would be highly appreciated. Thanks.

Hi, Please verify if the issue occur to all mailbox users. Do you have anti-virus application installed? Please try to run the command below to locate a black hole router: ping <var>computer_name or IP_address</var> -f -l 1472 If you cannot ping, then please try to follow the steps to fix the problem. Enable PMTU Black Hole Detection on the Windows-based hosts that will be communicating over a WAN connection. Follow these steps: 1. Start Registry Editor (Regedit.exe). 2. Locate the following key in the registry: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\tcpip\parameters 3. On the Edit menu, click Add Value, and then add the following registry value: Value Name: EnablePMTUBHDetect Data Type: REG_DWORD Value: 1 4. Quit Registry Editor, and then restart the computer More related information to share with you: How to Troubleshoot Black Hole Router Issues http://support.microsoft.com/kb/314825 Xiu

Hi, Please verify if the issue occur to all mailbox users. Do you have anti-virus application installed? Please try to run the command below to locate a black hole router: ping <var>computer_name or IP_address</var> -f -l 1472 If you cannot ping, then please try to follow the steps to fix the problem. Enable PMTU Black Hole Detection on the Windows-based hosts that will be communicating over a WAN connection. Follow these steps: 1. Start Registry Editor (Regedit.exe). 2. Locate the following key in the registry: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\tcpip\parameters 3. On the Edit menu, click Add Value, and then add the following registry value: Value Name: EnablePMTUBHDetect Data Type: REG_DWORD Value: 1 4. Quit Registry Editor, and then restart the computer More related information to share with you: How to Troubleshoot Black Hole Router Issues http://support.microsoft.com/kb/314825 Xiu