Re: authenticated email

Haren writes:

> If SMTP server uses certification authentication
> to trace all messages easily. And each mail adds
> the SMTP's server's public key and then is
> signed by the SMTP on the message, so when you
> receive it you know if the signature does not verify
> it has been tampered.
This is a truckload of additional overhead, though.  Not only that, but even
a slight modification of the signed text will invalidate all the signatures.
Then what?