Using an email service, Gmail for example, that tracks (and presumably reads) your incoming and outgoing mail is poor security judgement.
Following a California magistrate ruling on 19 April 2017, it’s suicidal.
Shaun Nichols covers the details in Nuh-un, Google, you WILL hand over emails stored on foreign servers, says US judge.
But the only part of the decision that should interest you reads:
…
The court denies Google’s motion to quash the warrant for content that it stores outside the United States and orders it to produce all content responsive to the search warrant that is retrievable from the United States, regardless of the data’s actual location.
Beeler takes heart from the dissents in In the Matter of a Warrant to Search a Certain E-Mail Account Controlled & Maintained by Microsoft Corp., 829 F.3d 197 (2d Cir. 2016), reh’g denied en banc, No. 14-2985, 2017 WL 362765 (2d Cir. Jan. 24, 2017), to find if data isn’t intentionally stored outside the US, and can be accessed from within the US, then its subject to a warrant under 18 U.S.C. § 2703(a), the Stored Communications Act (“SCA”).
I have a simpler perspective: Do you want to risk fortune and freedom on a how many angels can dance on the head of 18 U.S.C. § 2703(a), the Stored Communications Act (“SCA”) questions?
If your answer is no, don’t use Gmail. Or any other service where data can be accessed from United States for 18 U.S.C. § 2703(a), but similar statutes for other jurisdictions.
For that matter, prudent users restrict themselves to Tor based mail services and always use strong encryption.
Almost any communication can be taken as a crime or step in a conspiracy by a prosecutor inclined to do so.
The only partially safe haven is silence. (Where encryption and/or inability to link you to the encrypted communication = silence.)