Introduction

Many email clients and services use port 25 for SMTP to send out emails. However an ISP (Internet Service Provider) may block port 25 in order to prevent spamming by its customers. This article will show you how you can check to see if Port 25 is blocked on your network.

Before you start

This article assumes that you know how to get to a command prompt on your computer. If you need help with this, please see our KnowledgeBase article Using telnet.

Instructions

1. Type the following command:

   telnet example.com 25

2. View Results:
   If Port 25 is not blocked, you will get a successful 220 response (text may vary).

   Trying 64.13.192.208...
   Connected to example.com.
   Escape character is '^]'.
   220 cl34.gs01.gridserver.com ESMTP Exim 4.63 Tue, 24 Jun 2008 13:45:04 -0700

   If Port 25 is blocked, you will get a connection error or no response at all.

   Trying 64.13.192.208...
   telnet: connect to address 64.13.192.208: Connection refused
   telnet: Unable to connect to remote host

   TIP:

   You can use this same technique to check if Port 587 is blocked as well.  Just use the following command:

    telnet example.com 587

FAQs

Q: What can I do if port 25 is blocked?
A: You may also choose to use the alternate Port 587. All of our customers should contact their ISP (Internet Service Provider) if Port 25 is blocked.  In many instances, they will let you use their outgoing SMTP servers.

Resources

List of common SMTP Servers:

• AOL - smtp.aol.com
• Adelphia - smtp.blk.adelphia.net
• AT&T - mailhost.worldnet.att.net
• Charter Communications - smtp.charter.net
• Comcast - smtp.comcast.net
• Netzero - smtp.netzero.net
• PacBell - mail.pacbell.net
• PeoplePC - mail.peoplepc.com
• Verizon - outgoing.verizon.net
• Yahoo - smtp.mail.yahoo.com
• Juno - smtp.juno.com
• SprintPCS - smtp.sprintpcs.com
• SpeakEasy - mail.speakeasy.net

Additional articles to read:

• Troubleshooting SMTP problems
• Set up third-party email applications