I've just installed Norton 360 and I'm having trouble with the VPN, it is blocking outgoing emails in Windows Live Mail (incoming is fine. When I disable VPN, everything works as normal.
Yes, VPN may block this port due to security reasons. However if you wish to unblock it, you can simply go to settings in Norton, there you will see option of traffic rules, either you can locate port 25 there and check if it is blocked, if it is, then you can allow it from there. If you face any issues allowing it or finding it,you can create a new firewall rule allowing access to port 25.
I’m using Windows Live Mail 
How are you accessing your email? Web interface, or a local email client such as Outlook or Thunderbird? The link above only works for local clients by allowing the client to bypass the VPN.
I’ve just been in contact with my ISP and they are telling me that the VPN is blocking TCP port 25. How do I reopen this port? Thanks: Dave
Thanks but before I posted this issue, I read and I’ve already tried that. Thanks: Dave
You can try adding the email application in split tunnel under VPN settings to resolve this.
You can also look at resolution given here : https://support.norton.com/sp/en/in/home/current/solutions/v131881814 for better understanding.