How to tell which Receive Connector is answering

The simple answer is: modify the smtp banner so that you can see who responds.

On the server that you are connecting to:

•  Get-receiveconnectors 
• Look for the Identity field & note that.    
• Set-receiveconnector –identity “NameOfConnector” –banner “220 WhatEverYouWant”

Note:  the banner has to start with 220<space>YourText.  The 220 in the banner is the response code which lets the client know to continue the session.

Note:  This changes the actual smtp banner for an smtp conversation.  When you are done troubleshooting, you will want to remove this.

For  example:
The Exchange server name we will use is:  GCS3E2K7

• Get-receiveconnectors
• Look for the Identity field & note it for the connector that you want to change. 
  (The Identity of mine is:  GCS3E2k7\Default GCSE2K7)
• Set-receiveconnector –identity “GCS3E2K7\Default GCS3E2K7” –banner “220 My Default Connector”
• Just to be careful, I want to check myself and verify that I set this correctly. 
  get-receiveconnector –identity “GCS3E2K7\Default GCS3E2K7” | *
  Review the results.  The banner field is not populated with “220 My Default Connector” so I'm good.
• Next, telnet to that server and the banner will tell me if my default connector is the one answering the telnet session.
  telnet GCS3E2K7 25 answers with a Banner of “220 My Default Connector.”  

 So, I know without a doubt that my default connector is the one answering my telnet request.

 Why would you do this?  I have a perfect example for you.  My customer couldnt get mail flow to work from their Hub to their Edge Server.  The telnet session failed with:  5.7.1 Unable to relay.  We did all of the normal things that you check with an "Unable to relay" issue and none of that checked out.  Finally, we altered the banner on his receive connectors on the Edge server and were able to determine that when he would make a connection from his Hub server to the Edge server it was being answered by the wrong connector.