I had postfix up and running, and I think it was complete, although there was still a little testing to do. But at some point, it stopped accepting connections from my home computer. I tried to telnet to the mail server on port 25 and I get a timeout. But if I telnet into it from an iphone app from the cell network, i get the 220 message that it's connected. This happened once, and a few days later i was able to connect again for a few hours, but then it stopped responding again. Meanwhile, I can still connect from other locations.
I tried to watch the connection with tcpdump, and i can see the connection coming in from the cell phone but not from the home network. So by my first guess it sounds like the firewall is blocking my IP. but I can still access https from my home network, so it's not the firewall unless it's only blocking a certain port from a certain IP. I have asked the data center to check the firewall several times and they assure me that it's not what's blocking me.
Is there are setting in postfix that would deny a specific IP for a while? maybe because of too many failed auth attempts? I still don't think that makes sense because if that were the case I should see something in tcpdump, but i'm out of ideas.