We have an Exchange Server 2010, we just swapped out our old voicemail system and I'm trying to setup Toshiba unified messaging. in the setup I wants use to set up SMTP and use an email address dedicated to forwarding the voice massages to email accounts. When we try to use port 25 it will not deliver because our Exchange denies this port, when we try to use port 443 nothing happens and then it just gives up. The vendor is asking if there is a way to whitelist SMTP which is coming from internal IP: 192.168.1.8 to my exchange server 192.168.1.26?
And, here's a TechNet article that explains how to whitelist an IP address with Exchange 2010: