In this post, I'm going to tell you two different ways to check if your ISP is blocking outbound smtp port 25 .
The Easy way:
1. From your browser go to port25.icannotconnect.com
2. Click "Start Test"
The web app basically attempts to establish a connection from your computer to outbound port 25, and tells you if the connection was successfully established.
The Windows way:
1. Press "Start" type "cmd" and click on it.
2. Type telnet smtp.mail.yahoo.com 25
3. If you get a response similar to "smtp110.mail.bf1.yahoo.com" then your ISP is not blocking outbound port 25
This is similar to the previous method but uses the windows telnet client to check port 25 accessibility.