SMTP Service Not Available, Closing Transmission Channel

A client wanted to move a hosted Domino server to on-premises. After the initial build of the VM and configuration of the new Domino server was completed, I began the cutover process. Domino came up with the correct server identity and could be accessed via Notes and iNotes. However, when testing email, it was discovered that while outbound SMTP email was working, inbound email was not being received. Confirmed the DNS and MX records were properly updated. Added the following debug parameters to the server’s notes.ini and restarted Domino.

       • SMTPDebug=4

       • SMTPDebugIO=4

       • SMTPClientDebug=1

While the output on the Domino console was less than I had hoped, it did show that Domino’s SMTP listener received the inbound SMTP connection request, initiated greetings to commence, and then reported an error before the chat started. The connection closed with the error 421 SMTP service not available, closing transmission channel.

Performing an Internet search for this error only returned suggestions to increase the error buffer on the Domino server, which I did not believe was the correct path.

Taking a closer look at the server-side documentation in the Domino Directory, it was found in the Configuration\Web\Internet sites view that an SMTP Internet site document was configured. This document listed the TCP/IP address from when it lived at the cloud provider. The address was changed to that of the new internal TCP/IP address. After a restart of the Domino service SMTP began receiving email.

Lessons Learned…

1. Do not forget about SMTP Internet site documents when troubleshooting SMTP routing issues.
2. As a best practice, use hostnames vs TCP/IP addresses. Had the original configuration used a hostname Domino would have picked up the address change from the DNS and routing would have just worked.

Hopefully, if you receive this error due to a bad address in an SMTP Internet site document this post will help you resolve the problem quickly.


Leave a Reply