Misleading title. Nobody did the impossible on iOS, just did clever things within the available frameworks. Well done author, it works. But did you ask yourself "should I really do this?"

What I hope is going to prove truly impossible is doing anything like this without requiring the user to explicitly accept the configuration profile. Even so I expect they will trick many into allowing "enhancement" of their email.

LinkedIn has a history of abusing email. From the early days* where they would email all of the contacts on your machine if you didn't read carefully enough to today where you can click unsubscribe many, many times and still get "important updates". It's a wretched hive of scum and recruiters, and they will never get between me and my email.

*spoke too soon! looks like they still do it: http://community.linkedin.com/questions/10106/i-want-linkedi...