Anyone who's worked on the PGP project would be the first to tell you that PGP does not and cannot encrypt the email's metadata (to/from, subject, timestamps, etc).

All PGP does is encrypt the inner message body. All of the metadata that TLAs love to analyze is sent in the clear (at best inside a TLS connection, although the SMTP protocol unfortunately makes it incredibly easy for well-positioned network attackers to downgrade these connections to in the clear)

While not a silver bullet, anonymous remailers can strip out a lot of metadata. Mixmaster remailers can also help against traffic analysis.

While not as popular as they once were networks of remailers are fairly easy to spin up.

None of this has anything to do with the incorrectness of the assertion that PGP would “beg to differ” that end-to-end encryption of email is impossible. Playing 3-card monty with your message is something else entirely.