Outlook error 0x8004210B

Problem

Following is the error message in outlook.

Task 'demo@domain.com (1) - Sending' reported error (0x8004210B) : 'The operation timed out waiting
for a response from the sending (SMTP) server. If you continue to receive this message, contact your
server administrator or Internet service provider (ISP).'

Solution

It usually occurs when smtp port 25 is blocked by either your ISP or firewall in your local machine. You may check it by simply telnet'ing on port 25 on your domain.

In Start menu, click on Run and type the following.

telnet mail.domain.com 25

If the port is not blocked, you may get server smtp greetings like the following.

bash-3.1$ telnet mail.deru.net 25
Trying 140.99.9.2...
Connected to mail.deru.net (140.99.9.2).
Escape character is '^]'.
220-para.deru.net ESMTP Exim 4.51 #1 Sat, 22 Sep 2007 18:28:25 -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, you will get connection timed out error. If latter is the case, you need to check the firewall in your local machine. If firewall is causing the problem, you need to make necessary changes. Otherwise, it would be your ISP.

If you are a Deru customer, you may change the smtp port to 26. Otherwise, you may need to use your ISP's mail server for sending mails.