Deleting Draft emails

Try cancelling the move and then hold down ⌥ to apply “Message ▸ Delete Now”. This should prevent MailMate from moving the message and instead delete it permanently from the Drafts mailbox. There is no way to undo such an action.

Let me know if this does not resolve the issue.

(I don't know why the server does not allow moving emails to the trash, but if this is a general issue then I could consider adding a “Delete Now” button to the error message...)