[adrianba]

That's what ECPA says, but the Fourth Amendment does apply to e-mails as well as ECPA. Today, pretty much no significant commercial e-mail provider is going to give up e-mail contents without a warrant, even when over 180 days old.

In 2010, the Sixth Circuit held ECPA to be unconstitutional as it relates to email and compelled disclosure without a warrant (at least for large volumes of private email) [0]. This hasn't been tested at the Supreme Court, although the Warshak opinion has been cited approvingly, mostly because providers don't disclose content without a warrant so nobody has had a case to take up.

Carpenter shows 4A can protect metadata under some circumstances too (for more than 7 days of CSLI), even if law enforcement obtain a court order, which requires less evidence than a search warrant.

[0] https://en.wikipedia.org/wiki/United_States_v._Warshak