[snakes1100]

To trouble shoot the email system correctly, you need to first use the maintenance feature in the admincp --> Maintenance --> Diagnostics --> Email

You can also try the smtp option in vbulletin admincp --> vbulletin options --> email options

If neither option works, you would have to view your email log on the server and find out why email is not being sent out, this would require root access to the server.