The latest code commit is a big improvement... I added async/non-blocking loading with cancellation and a nice little spinner to the party -- so it feels more responsive.
Next up would be to combine the loading so that it loads the body mime types first and progressively loads the attachments. That is a bit complex as it might require (for the HTML view) supporting some sort of local http host for images, etc -- so that they
can be loaded progressively.
Not sure how far I want to go in making Papercut into .NET's Thunderbird. ;)