[…] The broad rights email providers claim for themselves has come to light following Microsoft’s admission that it read a journalist’s Hotmail account in an attempt to track down the source of an internal leak. But most webmail services claim the right to read users’ email if they believe that such access is necessary to protect their property.
[…] Google’s terms require the user to « acknowledge and agree that Google may access… your account information and any Content associated with that account… in a good faith belief that such access… is reasonably necessary to… protect against imminent harm to the… property… of Google ». Apple « may, without liability to you, access… your Account information and Content… if we have a good faith belief that such access… is reasonably necessary to… protect the… property… of Apple ».
http://www.theguardian.com/technology/2014/mar/21/yahoo-google-and-apple-claim-right-to-read-user-emails