I agree with Nick. It's good that there is a work around, but it feels convoluted. One would think Proton's native desktop app should be able to handle this without the need for another email client (Thunderbird).

This would be great. It is odd to me that the official method Proton suggests is to use a third party mail client, Thunderbird, and then link your Proton account there. This undermines their own mail client. In that same guide, they mention that MBOX is an industry standard file type but Proton Mail does not accept it. This seems like an oversight.