When my VPN is connected (ProtonVPN), I can’t send mail. Outgoing mail just sits in my outbox. I do receive mail normally. Proton has no answer for this. Can this be fixed so I can send mail while still using my VPN?
It’s your VPN that’s the issue. Most VPNs cause havoc with mail clients due to the way they work. You either need to try a different VPN or “don’t use them at all” when using Mail clients.
See the following thread on Proton VPN.