ISPs blocking smtp port 25

It is common to see that some ISPs blocking smtp port 25 to prevent other mail servers to send emails through them. It is easy to verify whether your ISP is blocking port 25 or not.

On your windows machine, click on Start -> Run, and type the following,

telnet domain.com 25

and click OK

If the smtp port is not blocked, you will get normal smtp greeting message similar to the following.

bash-3.1$ telnet deru.net 25
Trying 140.99.9.19...
Connected to deru.net (140.99.9.19).
Escape character is '^]'.
220-para.deru.net ESMTP Exim 4.63 #1 Fri, 21 Dec 2007 09:25:22 -0700
220-We do not authorize the use of this system to transport unsolicited,
220 and/or bulk e-mail.
quit
221 para.deru.net closing connection
Connection closed by foreign host.
bash-3.1$

Otherwise, the connection to port 25 on your domain times out.

If the port 25 is blocked, you need to use the ISP's mail server as outgoing mail server to send out emails from your email clients.

If you are a Deru Customer, you can still send emails using your domain, but using port 26 for smtp.

Following are the steps to change the smtp port to 26 on your outlook express.

1. Open Outlook express
2. Click on Tool -> Accounts
3. Highlight the account and click on Properties
4. Select Advanced tab
5. Under Server Port Numbers, change Outgoing mail (SMTP) port to 26
6. Click on Apply and OK to save the changes