They key to PGP e-mail security is that it provides full end-to-end encryption. The "path" you describe is actually flawed, and in fact may be overkill depending on your needs.
Hopefully, the below overview will help you see how the multiple layers of security you are suggesting would be applied.
- You start with your e-mail.
[Email]
- Your system encrypts the e-mail with PGP.
[PGP [Email] ]
- Your system puts the package into a secure stream addressed to your e-mail provider. (We'll say SSL.)
[SSL [PGP [Email] ] ] ]
- Your system sends that traffic to your trusted VPN gateway.
[VPN [SSL [PGP [Email] ] ] ]
- Once traffic reaches the VPN gateway, the VPN gateway forwards it along to your e-mail provider through the open Internet. However, this is not part of your trusted connection to the VPN gateway.
[SSL [PGP [Email] ] ]
- Your e-mail provider stores the message on their servers. Without intimate knowledge or agreements as to how the provider handles their data storage, you cannot assume that any additional encryption is used.
[PGP [Email] ]
- When the E-mail provider receives your message, they send it along to the recipient's e-mail provider. However, you cannot be sure that their provider's servers require connection security to receive e-mail or that there is any encryption used on their at-rest data.
[PGP [Email] ]
- The recipient contacts their provider's server to check their e-mail. However, you cannot be sure that the recipient's client software is configured to use a secure connection for this.
[PGP [Email] ]
- The recipient finally decrypts the e-mail and reads it.
[Email]
Strictly for the purpose of ensuring confidentiality of the e-mail message's contents, the VPN is essentially superfluous. In fact, so long as PGP remains unbroken and the keys you are using are trustworthy and un-compromised, every layer of security applied afterward could fail and the e-mail's contents would still remain protected in transit. You could be using an unencrypted connection to your e-mail provider over the clear Internet, from the sketchiest of coffee house hotspots, and your e-mail would still be protected in its travels. That's the point of end-to-end encryption - it's made so that the transfer medium does not need to be trusted, especially because it cannot be trusted.
If you're looking to additionally provide anonymity, then the VPN does have a purpose. However, to be fully effective, this requires that you do not provide any Personally Identifiable Information (PII) to your e-mail & VPN providers (E-mail headers still have to be sent in the clear, and you cannot trust the path between your VPN provider and the recipient. Your e-mail and/or VPN provider may therefore be forced by court order or other coercive measures to reveal your account info & connection logs.) and that you do not do anything over the VPN connection from which your PII can be directly obtained or inferred.
Of course, all this protection also relies upon yours and the recipient's systems being secure. If either system is compromised, all bets are off anyway.
In the end, you should always remember Law #9.