Using PGP over self-hosted email servers won't help you against a post-quantum adversary. While people have discussed post-quantum extensions to PGP, it doesn't exist yet. Similarly, while post-quantum TLS _does_ exist, it was only just implemented in OpenSSL; I doubt Postfix supports it yet.
So you're in an even worse post-quantum situation with email, even if you end up with TLS-encrypted PGP-encrypted messages, you're still not post-quantum secure.