win11 send/receive issues

Dump the VPN if you are having connection issues. There have been and will be issues with VPN product and mail providers that monitor your location etc to decide if you have been hacked. As the sole purpose of a VPN is to disguise your connection and physical location they tend to drop connection attempts, fail to connect and ask for password oAuth re-validation frequently. The exact scenario depends on the VPN and it's quirks. Some VPN products do not support email at all. Others allow you to exempt certain programs like mail clients from the VPN. I doubt anyone here compiles a list of known issues with VPN's. None of them are much good with email appears to be the general consensus. That includes the Mozilla VPN. Essentially most folk also have the same mail account configured on multiple devices at the same time and the providers say your phone is in Durban and you desktop is in Cairo. Something is wrong perhaps. I am simplifying this considerably. But essentially you need to deal directly with your VPN provider and find out how they suggest you connect to specific mail providers and ports if mail works without the VPN and does not with it active. A quick websearch on surfshark dropped these instructions my way. https://support.surfshark.com/hc/en-us/articles/10447995732114-I-can-t-send-emails-while-connected-to-Surfshark#Mozilla-Thunderbird although 2 years ago they said they also blocked port 587 You do say you are now using Windows 11 and previously used windows 10. That implies to me you have a new antivirus. Personally I just use windows defender because it is less troublesome that the paid third party junkware that comes preinstalled on new computers so frequently these days. One of the principal causes of mail client connectivity failure is antivirus. Most have specific instructions on how to break the chain of trust used in encryption so they can function using their self signed certificates for email scanning. Defender does not scan email. It is one of the reasons I use it.