iCloud email users won't receive messages with certain words in them – and Apple doesn't tell anybody when it happens.
While few people will miss the emails being censored – those containing the phrase “barely legal teen” – it’s unknown how many other things are being blocked. There’s no public list. And it means that Apple is scanning the contents of your emails.
Emails containing the targeted phrases are simply not delivered, although the sender receives no notification. Macworld tested it by sending an email which read, “My friend’s son is already allowed to drive his high-powered car. It’s ridiculous. He’s a barely legal teenage driver? What on earth is John thinking.” and one that swapped the phrasing to “barely a legal teenage driver.”
The first never showed up, while the second did. That at least means multiple-word phrases have to be used in the same exact way they’re filtered to trigger the censor bot. We also know attachments can’t include the censored phrase, because that’s how this originally came to light – a film scriptwriter was trying to send a script that included a scene where a character sees a porn advertisement.
Apple’s right to do this is spelled out in the terms of service (which virtually nobody reads): “Apple reserves the right at all times to determine whether Content is appropriate and in compliance with this Agreement, and may pre-screen, move, refuse, modify and/or remove Content at any time, without prior notice and in its sole discretion, if such Content is found to be in violation of this Agreement or is otherwise objectionable.”