Incoming SMTP blocked by ISA

I ran into an issue with my recently deployed ISA firewall. It was blocking
any STMP incoming traffic. This made it so my Exchange users could send 
email just fine but could not receive any incoming email. I checked the 
Event Viewer and saw this:

Event Type:        Warning
Event Source:    Microsoft Firewall
Event Category:                None
Event ID:              14090
User:                     N/A
Description:
The server publishing rule Exchange POP3 SMTP Server, which maps 
192.168.5.32:25:TCP to 183.9.124.120:25 for the protocol SMTP Server, was 
unable to bind a socket for the server. The server publishing rule cannot 
be applied.   

To resolve this I had to make a simple change to my Exchange SMTP rule in ISA. First go into the ISA management console. Find your SMTP rule for incoming traffic. Right click on it.

Select properties. Then go to the “To” tab. Be sure to select “Requests appear to come from the ISA Server computer

Click ok and then apply the changes to ISA. This should fix the issue and you will not see the warning in event viewer anymore.

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