Blocked Port 25 Workaround

Recently, I switched to AT&T DSL. I’m quite happy with the price of $19.95/month. Of course, there was a drawback; they block port 25, the port used to send email. I figured that out after an hour of searching. There are a few solutions for this. Here are my findings.

Update: I use sendmail on a linux  server to run my email.

Solution 1: Change the listening port
This is the most obvious fix, and the one I implemented. You need to admin your own server to do this. Using sendmail, it’s only 2 lines in sendmail.mc:


define(`RELAY_MAILER_ARGS', `TCP $h 2525')dnl
define(`ESMTP_MAILER_ARGS', `TCP $h 25')dnl

The first line changes the smtp port to 2525, and the second line changes the outgoing smtp port back to 25. Without the second line, no email will go out.

Note: when editing the sendmail.mc, you need to compile it by running make or m4 sendmail.mc > sendmail.cf. After compiling it, restart the sendmail daemon. DO NOT EDIT sendmail.cf!

Solution 2: Use a proxy
There are plenty of services out there that will proxy, or relay, for a fee. I am sure there are proxies that are free, but I wouldn’t trust them to keep my information private for a second.

This solution doesn’t require you to have admin rights on the server and it is a lot easier. Each proxy setup is different, so follow the instructions they give.

Solution 3: Don’t send email with that account
Not the best solution, but you can get a yahoo or gmail account for free. You can still receive email from any account. This is probably not acceptible for most people.

Solution 4: Switch to another ISP
This is always an option, even if it means downgrading to dial-up. The only reason why I am keeping AT&T is because of the price.

Well, I hope that you found this information helpful. Happy e-Mailing.

Networking Day 5: Port Forwarding

Today is all about port forwarding.  This is needed when you want to make a specific service available to anyone on the internet.  That service could be a game, a web server, or even Yahoo Messenger.

Ports
Anytime you connect to a server, you are connecting to a specific port. The server listens on that port for incoming connections and respond appropriately. Different port numbers are for different services.  A few examples include:

  • 80 — http
  • 21 — ftp
  • 25 — smtp (sending email)
  • 110 — pop3 (recieving email)

Before you begin the setup, you should find out what port needs to be opened.  You can figure this out by the manual or a quick internet search.

Setting up a static IP
This is necessary for most port forwarding.  Please review Day 2: Subnets for information on selecting an IP address to use.  The static IP must be in the same subnet as the dynamic IP.

Also, make sure that the DHCP on your router will not give out this IP address.  All routers will have a range of IP addresses.  If the range starts at “.100”, you can use “.99”. Also, if the range ends at “.199”, you can use “.200”.

Setting up the forwarding
Log into your router’s admin interface.  There should be “port forwarding” or “port address translation” in the menu, click this.  On this screen it should have somewhere you can enter the port and ip or a link to click to get to enter that information.  Enter the port and IP, click save, and you’re done.

Don’t forget to get your public IP address from a service like WhatIsMyIP.com.