Can I use iOS 7 blocking to block iMessages between Apple IDs instead of phone numbers?
Yes, on iOS 7, you can block someone from sending you an iMessage from their Apple ID. When you block a contact from sending you texts, it applies to SMS (sent to phone number) and iMessage (sent to phone/Apple ID email). Currently this works only on iOS devices. Any iMessages received on a Mac are not blocked.

How it works is described in detail here - Silence is Golden: A Guide to Blocking Calls and Texts in iOS 7


  What about texts?
  
  If you’re sending a text, it will look like it was delivered. If you’re sending a message to someone who has blocked you, and you’re using iMessage, it will say “delivered” — exactly like a text that went through.