The next thing you know they will be looking at the CC and REPLY-TO headers! When will it stop?! Irony aside, I don't think this is any worse than for instance

The next thing you know they will be looking at the CC and REPLY-TO headers! When will it stop?! Irony aside, I don't think this is any worse than for instance a text editor detecting programming languages by, yes, parsing the content in order to provide a useful function to the user.