

My guess is that whatever VPN server your connected to had someone else who was spamming or doing something else they weren’t supposed to. This caused the email addresses associated with that IP to be flagged.
One of the drawbacks to a VPN is you share your IP with strangers who sometimes do stuff you get penalized for.


Why? Both of those options are worse. You can’t be a privacy respecting service and not allow VPNs. If you do allow VPNs, it is going to force you to sometimes blanket ban an IP because bad actors use VPNs as well.
Typically this only happens on free VPN servers because people who abuse these services also realize they are going to get banned. The easiest solution is to use a premium VPN or signup with your actual IP address (depending on your threat model).