TLS1.2 for SMTP end-to-end is obviously a good thing, but it has its own problems aside from all of the crap we've been piling on top of SMTP for 20+ years (SPF, DKIM, DMARC, TLS1.2, etc) for ISP mail server operational reasons.

At some point that mail has to go into storage somewhere so it can be accessed by a user/client via IMAP, and that's where the subpoena/national security letter/warrant/FISA court request will go. To whatever location the disk storage resides at.