When you connect to AdBlock VPN, you’re creating a point-to-point connection (or a tunnel) between your device and our VPN servers. This allows your device to create an encrypted connection without our servers, which in turn forwards that encrypted data back to the website servers.
Unfortunately, this means your device is temporarily considered “excluded” from your local network while you're connected to your secure VPN tunnel. Because of the way a device connects to a VPN, you may not be able to connect to local network devices, such as your printer. This prevents local email clients like Outlook and Thunderbird from sending and receiving email as well.
This is a symptom of using any VPN service, so the only solution is to temporarily disconnect from your VPN any time you need to use your local network devices or local network email.