> How would that help? They'll just get a warrant for those.

In terms of e-mail, any service that encrypts at rest and doesn't maintain the key can only hand over encrypted data. ProtonMail would be one example.

>How would that help? They'll just get a warrant for those.

If the business is not based in the US, it will make getting a search warrant much more difficult. Your (e.g.) Protonmail account is less likely to be subpoenaed than your Gmail.

Even if user data were seized, it would be impossible to decipher because of ProtonMail's encryption. Unlike Gmail or Outlook, email you send with ProtonMail is encrypted before it's sent to the ProtonMail servers.

Then they would seize his phone and use that to decrypt the email.

Or order him to turn over his own email.

> Or order him to turn over his own email.

Which they could have done in this case. So why subpoena Google?

Apparently some concern he might accidentally click delete instead of duplicate. Non technical user and all. Google staff have more training.