Since social posts are usually timely, not to mention pretty easy to create, making a copy of one may not give you any advantage. Email's are a bit more complex to recreate, so we have that functionality built into your account.
To make a copy of any email message you've already created, whether it's been sent or in draft form, just click the box next to the name on the Messages tab, then select the Copy button in the upper right hand corner. We'll make a copy for you that you can edit. It's name will be "Copy of" plus the original email name, but you can change it if you like.