I have two Xfinity (comcast.net) email accounts and a gmail account on Thunderbird, which I am using for the first time. The gmail works fine. The comcast.net accounts receive okay but whenever I try to send it takes me to the Xfinity sign-in page for a password. When I type it in it says "You don't have permission to access "http://login.xfinity.com/login" on this server." The password is correct as I was able to set up the accounts and it pulled in all my messages. I am not a very proficient user so please make it as simple as possible. Thanks in advance.