Do you really want to hand over your private PGP key to 3rd-party company? I never ever won't do that. If I will use PGP key for web email service, it is only when the service provider gives a way to communicate with my local machine so that the email text is SIGNED IN MY MACHINE and send it back to the email provider, then send to the recipients. For encryption, it can be done with public key of the recipients.