The Snowden leaks themselves show they have to get access to American email via the FISA system.
They buffer pretty much everything for a while so they can backtrack a couple days but that information isn't being filtered through a search algorithm.
Nah, you're misunderstanding. The FISA court is only for formal intelligence filings which could be used for active casework.
Assuming they play by the rules (they don't, but anyway...) all they'd have to do to get your emails anyway is ask GCHQ for them. GCHQ isn't American, so they didn't break any laws by grabbing the content and metadata for all your communications. GCHQ passes the data to the NSA, and boom, they have your data. Legally, with no FISA warrant.
The FISA court is a rubber stamp, anyway-- look at their approval rate.
This is an underappreciated concern regarding spy agencies. What difference do laws that prohibit domestic surveillance make if spy agencies can just enter reciprocal agreements to share data?
If you're running an agency in the US that can't spy on Americans, you can make a deal with a similarly bound agency in the UK - they get your UK data, you get their US data, and you have all the US data you want even if you didn't collect it.
They buffer pretty much everything for a while so they can backtrack a couple days but that information isn't being filtered through a search algorithm.
Your email isn't in their database.