In 1986, the United States Congress updated the Omnibus Crime Control and Safe Streets Act of 1968 by enacting the Electronic Communications Privacy Act which included an updated "Wiretap Act" and also extended Fourth Amendment-like protections to electronic communications in Title II of the Electronic Communications Privacy Act, known as the Stored Communications Act.
In Carpenter v. United States (2018), the Supreme Court ruled warrants are needed for gathering cell phone tracking information, remarking that cell phones are almost a “feature of human anatomy”, “when the Government tracks the location of a cell phone it achieves near perfect surveillance, as if it had attached an ankle monitor to the phone’s user”. and that
[cell-site location information] provides officers with “an all-encompassing record of the holder’s whereabouts” and “provides an intimate window into a person’s life, revealing not only [an individual’s] particular movements, but through them [their] familial, political, professional, religious, and sexual associations.”[5]
AND
From https://www.legalmatch.com/law-library/article/e-mail-and-wa...
Are there Any Laws that Protect Your Email Privacy?
Under the Electronic Communications Privacy Act (ECPA), police can access emails without a warrant if the emails are stored in the cloud and at least 180 days old. However, this law is outdated and lawmakers are attempting to pass the E-mail Privacy Act. This would update the ECPA by requiring warrants for all email searches. At the moment, in July 2018, the ECPA has yet to pass.
E-mails that are in remote storage and opened or older than 180 days do not require a warrant. Instead, the police only need to obtain an administrative subpoena. Administrative subpoenas are issued by federal agencies without any approval by a judge, so they are much easier to obtain.
So.. run your own email server in your basement if you're concerned (which would require a warrant). Or try end-to-end encryption solutions.