I posted a while back on this issue, still having the same issue and am trying to set up sbs server with exchange.  Have got ports 25, 80, 443, 3389 forwarded in router on vodafone broadband with static ip.  Every port except for 25 works.  I can telnet to port 25 internally and it works, but externally is a no go, connection failed.  So tried mapping a random external port (8977 in this case) to port 25 internally on the sbs server and it worked I could telnet to port 8977 externally and got a reply from the smtp.  Have even tried another router to get 25 working, but whatever I do I can not get port 25 on its own to work.  I know Vodafone are obviously blocking it, this is a business connection with a static ip, so why is port 25 blocked?