Checking your outgoing mail server (Is Port 25 blocked?)


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 search Google on how to use telnet.


This article is provided as a courtesy. Installing, configuring, and troubleshooting third-party applications is outside the scope of support provided by Linuxweb.


  1. Type the following command:
    telnet 25
  2. View Results:
    If Port 25 is not blocked, you will get a successful 220 response (text may vary).
    Connected to
    Escape character is '^]'.
    220 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.
    telnet: connect to address Connection refused
    telnet: Unable to connect to remote host


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

     telnet 587


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.


List of common SMTP Servers:

Cell C
Internet Solutions (ADSL) (56k dial up on IS)
MWEB (ADSL) (56k dial-up)
SAIX (Telkom)
Telkom (ADSL) (56k dial up)
Web Africa

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