As you are no doubt aware, Muggles cannot use "Owl Post" and have to rely on "postmen and postwomen" to deliver their mail! How inefficient! However, it has been brought to my attention that the Muggles now have a thing called an eCard!!?  For your education I have included a few links to such sites, so that you don't appear ignorant when your Muggle friends talk about them! Obviously they are not as quick or efficient as our trusted Owl Post!