Provide full email for drag and drop
Right now, when dragging an email out of the email list, a file path to the email gets transferred.
As an application, I'd like to get hold of the email, however. The path may not be available to me (as an app) because I run in a sandboxed environment.
AFAIK, the DnD protocol allows for postponing the expensive operation of loading the email into memory and putting it into the drag-buffer, so the full email could only be given to clients who request that content type.
Note to self: this code seems relevant: https://github.com/GNOME/evolution/blob/4e84818c513542a66aa20beb25e7d97f3f1792e9/src/e-util/e-attachment-view.c#L846