Short answer: everything is encrypted. So they could forward it in theory, but it would be unusable downstream anyway. The way you'd have to do it is set up the decryption email bridge on a client and set up some manual forwarding after that on the client side.
Happy proton user that doesn't need this feature, but gets why it would be frustrating for others who want a clean way to move off if they decide to.
Happy proton user that doesn't need this feature, but gets why it would be frustrating for others who want a clean way to move off if they decide to.