The relaying MTA (in this case sendmail) had ident-check (RFC 1413) enabled. This means that when an incoming connection occurs, it sends a request to the client on port 113. If this client does not answer within 5 seconds (default timeout) it continues with the request.
With the ident-feature turned on, the MTA logs the following error after the tcp connection gets shut down: backup01.admin [172.16.0.7] did not issue MAIL/EXPN/VRFY/ETRN during connection to MTA
The problem can be solved in different ways:
1. Install an identd on the client hosting archttp and allow it in firewall.
2. Actively refuse connections on tcp/113 if identd is not available on the client hosting archttp.
3. Disable the ident check in the MTA.Tags: Archttp, Windows 2008