subscribe to newsletter link not working

hello,

how do we configure nop commerce subscribe to newsletter for nop commerce 1.9.

Store Admin Email: gmail address
Store Admin Email Display Name:
Host:  smtp.gmail.com
Port:  587
User:  [email protected]
Password:   Password
Enable SSL:  Yes
Use default credentials: UN-CHECKED

on sending the test mail we get the following error ;

"Request for the permission of type 'System.Net.Mail.SmtpPermission, System, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089' failed."

Regards,