> Even if your provider stores and transmits only encrypted email data, once sent it does not maintain that guarantee while being passed by another entity's MTA.

What? If Alice encrypts an email to Bob, using Bob's PGP key on her laptop, then it doesn't matter how many MTAs that email passes through, the email stays encrypted at every hop.

> it could wind up being archived to tape

I guess you're saying that an encrypted email could travel through a provider that keeps a copy of it in the hopes that quantum computers will one day be cheaply available enough that they can crack the private key and read the email.

That seems expensive (and illegal) for a company to do just on a whim (assuming the sender and recipient are periodically deleting old emails), and I'd like to think that a judge would turn down a request for a warrant that covers data that won't be readable for a decade or more.