Causes and Resolutions

There are multiple possible reasons why E-mail would be unable to send messages to external email addresses.

Cause 1 - Outgoing connections to port 25 blocked by your personal firewall 

The first and easiest thing to check is to make sure that your personal firewall (like ZoneAlarm, Norton Security) is not blocking outgoing connections on port 25. 

To test this, go to a command prompt on your PC and try to telnet your own mail server. Type following:

telnet mail.yourdomain.com 25

You should get a response like this:

220 mail.rapidvector.com

If you get a response starting with '220' you can just type 'quit' to end the session. 

If the connection fails then you likely have outgoing connections on port 25 blocked by your personal firewall. Try turning off your personal firewall or AntiVirus on your PC and try telneting again. If you succeed then you can reconfigure your firewall to allow Outgoing TCP Port 25 into your firewall.

Cause 2 - Outgoing connections to port 25 blocked by your ISP

If you believe that your ISP is blocking SMTP traffic then configure your outlook to use alternate SMTP port 49.