Configure error for SharePoint alerts

In my SharePoint site I enabled alerts. The problem is that the alerts are activated for the users, but no emails are send to the users. I configured the 开发者_StackOverflowcentral admin in correct way. I went through Troubleshooting SharePoint Alerts, but no use. What is the actual one that is causing this?

I set the alert frequency to immediate.

From first look I feel the problem is with your server where MOSS is installed. Kindly get your IT infrastructure team picture as it seems from your server you are not able to send mails. Follow the steps in Send Email via Telnet to confirm what I'm saying.