Hi David,
At a very basic level, an Email can be shared as an Email - so we have an option of forward to friend(Which, in essense is Sharing the email in your social circle). The reason we talk about landing pages is becasue that's an asset which is eligible to have "Social Share" options - It's open to everyone, which can be shared by everyone. On the other hand, Emails are of a personal nature - therefore, no, this is not a feature of Emails. It's not supposed to be!
Hope this helps!