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. Here is how you can check to see if port 25 is blocked on your network.

1. Type the following command:

   telnet mt-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 mt-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

 telnet mt-example.com 587

What can I do if port 25 is blocked?

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. Depending on your service you may have an alternate choice.

• (gs) Grid-Service customers may use the alternate port 587 to get around a blocked port 25. They only need to make this change in their email client.
• (ss) Shared-Server customers have the option to migrate to the (gs) Grid-Service so they may use port 587.
  
• (dv) Dedicated-Virtual customers can review our article on changing the SMTP mail port.

Notes/Supplemental Resources:

• Sending Email via an SMTP Server
• Email Program Setup Guides 
• ISP Outgoing SMTP Server Listing

Revisions:

2009-02-02: Updated article to point to kb 1634 on how to get to a command prompt.