Today, I discovered that SmarterMail isn’t receiving emails from other hosts outside my local network. I first logged on to SmarterMail as admin. Nothing apparently wrong with the mail system. I next opened up a Command Prompt and tried to telnet to mail.larrybrouwer.com 25 and it worked fine. Next, I logged on to a remote server and again attempted to telnet to the smtp service. This time, nothing happened.

My thoughts then turned to firewall issues. So I checked to make sure that the firewall wasn’t blocking port 25. It isn’t, but just to make sure, I disabled the firewall and again tried to telnet into the email server on port 25. I’m still not able to log in.

I next suspected my D-Link DIR-655 router as the problem. I logged into the router and checked the Virtual Server settings. The the router settings look fine. I then remapped port 25 to port 80 just to see if I can get through to the web server. Re-mapping didn’t work. Now I’m really puzzled.

Still thinking that it’s a router issue (since remapping ports didn’t work), I looked at the Firewall Settings. The TCP Endpoint Filtering is set to ‘Port And Address Restricted’. I changed it to ‘Endpoint Independent’. I also enabled anti-spoof checking. I then rebooted the router. After re-logging back into the router, all of my Virtual Servers have disappeared. I re-entered them. I then attempted the telnet test to port 25 again. This still did not help the problem.

I next attempted to set up the DMZ on the DIR-655 for my web server. This should allow all traffic to flow to the web server. After re-booting, I again tried to telnet to port 25 with no success. But I am now able to telnet to port 110 (pop3).

So, by now I’m beginning to pull my hair out. What’s going on here? Well, I finally figured it out when I changed the default port for SMTP from 25 to 587. Once I did that, I was able to telnet to that port fine. So, my conclusion is that my ISP is blocking port 25 traffic. I verified this by Googling on ‘Comcast Blocked Ports’, and I got several links describing numerous ports that Comcast is blocking. The blocked ports include: 25, 68, 135-139, 445, 520, 1080, but may vary by location.

I verified this by attempting to telnet to an outside email server at port 25, and indeed it did not respond, but port 587 did respond fine.

I then went into my Comcast email account to check my messages (something I rarely do), and sure enough, there is a message “Customer Security Assurance Notice” which tells me that they’ve block port 25. I know why they did this! see my prior post here. This is a major bummer, and I read many posts left by upset Comcast customers.

I found one post that says the way to get this quickly resolved is to contact the Comcast Customer Security Assurance Center directly at (856) 317-7272 and avoid contacting the normal Comcast Internet Support channels. So I did this, and spoke to a very nice technician, and he said he would unblock the port within 15 minutes. Great news! It was actually completed within a minute of hanging up the phone with Comcast.

I then proceeded to turn on my Server’s firewall, and to configure SmarterMail back the way it was prior to all of this happening!

My next problem occurred when I attempted to send a test email from my web server to my Yahoo account, and it bounces back saying that Yahoo is not accepting messages from IP addresses on Spamhaus PBL. I did a Google search and found this article, How can I remove my IP address from the Spamhaus Database? So I went to Spamhaus and entered my IP address, and it came back with a hit on Spamhaus. I then clicked on the link to resolve the issue, and it came back stating that since I’m a Comcast residential customer, it can’t be removed from the list. Bummer!

So this means, I can receive emails, but I cannot send them. I will continue this tomorrow.