In early February I noticed that I could no longer send email from my home computer. It is a Windows machine and as far as I knew, the rest of the family on Macbook Pros, had no issue. I also seemingly had no issue on my Macbook Pro. The problem seemed to be isolated to my Windows 7 Desktop machine.
I uninstalled my email client and reinstalled it to no avail. I finally removed the hard drive and installed a new one, upon which I reinstalled the operating system from scratch. Still no e-mail. I was stymied.
Then last night, my wife said she hadn't been able to send email for a while. My daughter piped up and said, "Oh yeah... me too". I got to work troubleshooting in earnest. I started by trying to send email from my Macbook Pro. No dice. Then I turned on my wifi app on my Android and connected my Macbook to it's internet connection and was able to send without worry. Turns out I was using my Macbook email only while at work on their wifi network connection. I just hadn't noticed the problem on the macbook while at home.
After a little more debugging, (telnet 220.127.116.11 25) I discovered that port 25 was being blocked by my ISP. Apparently Qwest had just decided to block that port for me, with no notice, or warning or anything. Just BAM! blocked.
I called them and informed them of my displeasure. The tech apologized and said that the FEDERAL GOVERNMENT MADE THEM DO IT! Well of course that was a lie. The federal government doesn't regulate them to that degree. They decided to do it on their own in order to block spam from customer's computers that had been infected with a virus. I understand the policy, but what I don't get it the decision to just block port 25 with NO WARNING!
They were kind enough to remove the block for me and after resetting my router, the problem was fixed. If you are on Qwest DSL and don't have a static IP address, and can no longer send email. Port 25 filtering has likely been activated on your account. Call Qwest and ask them to remove the filter and they will.
Update May 10, 2011:
My eighty year-old neighbor came over the other day, describing problems he was having with his email. I went over and had a look, and sure enough. Internet connection was fine, he could receive email, just not send it. After a call to QWest to have them turn off the port 25 block on his account, he was back in shape. Apparently QWest is applying port 25 blocking to groups of people at a time. Clearly my next-door neighbor and I are on the same subnet, but my port 25 was blocked months before they blocked his.
What is an eighty year-old guy supposed to do if he doesn't have a techie for a neighbor? Shame on you QWEST!