But it does, and it's a common issue with VPNs. You should see what settings are in the VPN that bypasses checking email. This is a common issue posted here. The problem is not Thunderbird. It's by security enforced by email providers. Messages sent under VPN have IP addresses that are NOT within the IPs of the email provider - and they are then repelled.

I found the issue and this works: Switching the protocol to OpenVPN and changing it to UDP. Here is the link. https://support.nordvpn.com/hc/en-us/articles/20465552867345-Switching-protocol-to-OpenVPN-UDP-or-TCP#Windows

Similar issue posted at https://support.mozilla.org/en-US/questions/1497583