Port Error insufficient permission

I am getting an error in web.config: 
Parser Error Message: Insufficient permissions for setting the configuration property 'port'.   The port number 587 is correct for my email provider. Here is web.config:  
<system.net> <mailSettings> <smtp deliveryMethod="Network" from="name@email.com"> <network host="smtp.email.com" userName="name@email.com" password="pass" port="587" EnableSsl="true" defaultCredentials="false" clientDomain="domainname" /> </smtp> </mailSettings> </system.net>