Microsoft is not unique in claiming the right to read users' emails – Apple, Yahoo and Google all reserve that right as well, the Guardian has determined.

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.

Microsoft's own terms of service allow the company to access content "when Microsoft forms a good faith belief that doing so is necessary [to] protect the… property of Microsoft". It made use of that right to read the email of an un-named journalist who had allegedly taken possession of the source code to Windows 8 thanks to an internal leak at the firm.

Following the revelation that Microsoft could, and did, read users' email, the firm's deputy general counsel told the Guardian that it would be tightening up its privacy policy. The new rules require an internal and external legal team to review any internal requests for access, and commit the firm to increased transparency over future requests.

Yahoo, Google and Apple too

But other major email providers reserve exactly the same rights. Yahoo requires users to "acknowledge, consent and agree that Yahoo may access… your account information and Content… in a good faith belief that such access… is reasonably necessary to… protect the rights… of Yahoo."

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".

Of the major webmail providers, only Microsoft was prepared to share the internal procedures they have in place governing who can access users' email without a court order and what reasons they must give to do so. Yahoo declined to comment. Neither Apple nor Google had responded to requests for comment ahead of publication.

"The problem is, this is a technically legal activity that we all agree to when we sign up to certain cloud services – whether knowingly or not," says Charlie Howe, director, EMEA at Skyhigh Networks, a cloud security software firm, of Microsoft's snooping.

"For instance, I would guess that most people don’t actually read the full Terms and Conditions before using a new application, and they would probably be surprised by what they are actually agreeing to when they click the ‘accept’ button on certain cloud services."

• Microsoft has tightened its privacy policy for emails after admission it read journalist's messages