That probably depends on whether your ISP's mailserver uses opportunistic encryption. Any email I send to Google from my mailserver is always sent over a TLS-en

That probably depends on whether your ISP's mailserver uses opportunistic encryption. Any email I send to Google from my mailserver is always sent over a TLS-encrypted connection for instance, because Google's mailservers agree to encrypt where possible. In this scenario, the NSA wiretaps will get direct access to any email sent over unencrypted connections to the ISP mailserver, but they'll have to work harder to get at the encrypted data. Of course, as we know they've suborned the encryption used by many, many organisations so this is no guarantee of protection against an NSA fishing expedition, but it's a lot better than nothing.