Apple records a log of which phone numbers you typed into their iPhone for a message conversation, along with the date and time when you entered those numbers as well as your IP address. Apple records each query in which your phone calls home to see who’s in the iMessage system and who’s not. The Intercept obtained the document, titled ‘,’ about Apple’s iMessage logs as part of a much larger cache originating from within a state police agency. Apple says it does not have access to the contents of iMessage conversations or prove that any communication actually took place.
Source: https://thehackernews.com/2016/09/apple-imessage.html