If you're unable to send and receive emails and the VPN is on, check if your email client is using port 25 to communicate. The VPN blocks port 25 because it is an unsecured port commonly used for email spam.
To resolve this issue, contact your email provider who can assist you with setting the correct port number on your email client.
Note: You should not encounter this issue if you are using a web browser to send and receive emails.