Here is my issue: I'm attempting to host an Exchange 2013 server at my home. However, AT&T blocks port 25 outbound to prevent users from spamming.
My solution: I have a VPN provider who has opened port 25 on a specific VPN server and will allow me to send my email through them.
My new problem: Exchange can send email fine, but it won't receive. I've done some trouble shooting and here is what I've come up with. Exchange will allow telnet connections from my local network (192.168.0.0/24) over port 25 and all of the other receive connectors while the VPN tunnel is up, but it won't accept external connections (wireshark shows it receiving the SYN, but Exchange never ACKs them). If I tear down the VPN tunnel, Exchange gladly accepts telnet connections from anywhere (internal, and external), but I'm now unable to send email, because of AT&T.
Anyone?