I am having a strange problem on my Exchange 2010 server. When I attempt to send mail to one specific domain, the message times out. I have done some troubleshooting with IT staff from the recipient domain and an attempted Telnet or SMTPDiag connection does not even hit their firewall. We have also checked with both of our ISP's and nothing is being blocked. I then discovered a Telnet and SMTPDiag connection works as expected from 32-bit machines (Both XP, Server 2003 and 7). I did some research on this and thought it may be fixed by disabling TCP/IP Autotuning. I tested this on a 64-bit Windows 7 machine and after a reboot a successful Telnet connection was established. I attempted the same fix on my Exchange server (Sever 2008 R2 64-bit) and the connection still failed. Please assist!!

Single domain? Just send email to that domain through your ISPs SMTP server as a smart host. Email is always a best effort and for whatever reason the connection cannot be made. Most likely an error somewhere between you and them. Simon. Simon Butler, Exchange MVP Blog | Exchange Resources | In the UK? Hire Me.

Can you point me to some instructions on how to accomplish this with Exchange 2010 and Comcast Business Class? Will this change affect the flow of other outgoing mail?

You will need to find the SMTP server address for Comcast. It will be on their web site somewhere. Then create a new Send Connector. In the wizard set the type as Internet and then when asked for address space enter the domain you are having problems with. It will then ask for the smart host, enter the address from Comcast. As long as you only enter the domain/s that you are having problems with, other email will not be affected. Simon. Simon Butler, Exchange MVP Blog | Exchange Resources | In the UK? Hire Me.

This seemed to work. Thank you for your help.