If you haven’t yet been hit by iMessage spam, you’re lucky: It’s awful. And it’s even worse when you realize that the spammer can know with certainty that the unwanted message really was delivered to you. As first noted by MacStories, Apple recently posted a way to deal with unwanted iMessages in your inbox.
Here’s the skinny.
When an unwanted, spammy iMessage arrives, first take a screenshot. (If you got the iMessage on your iOS device, press the Home and Sleep/Wake buttons at the same time. If you see the spammy iMessage on your Mac, use Command-Shift-3.)
Apple also needs to see the full email address or phone number of the person you received the spammy message from. You can either screenshot that data too, or copy and paste it.
Once you have all those details assem …
Source: Mac OSX Hints