Tobias Rundstrom supplied a patch to ssmtp to enable secure mailtransfer
between your local (ssmtp) machine and the mailhub. It also supports
authentication with RSA keys, to enable you to (if you patch the MTA on
the mailhub) have RSA key checks on all relay mails.

He wanted this so that he could have the same SMTP server on his laptop even
when he moved around on different networks. As he said - "I could have used
postfix as I did on my mailhub, but that was overkill, so I patched the
smallest program there was :)"

information about smtp over ssl for postfix is avalible at:
http://www.aet.tu-cottbus.de/personen/jaenicke/pfixtls

How to use this:
I had to add the following config directives:

UseTLS=YES/NO
Set this to yes and ssmtp will try to connect with SSL to the remote machine.

UseSTARTTLS=YES/NO
Do a EHLO/STARTTLS before starting the SSL negotiation (see http://www.ietf.org/rfc/rfc2487.txt).

UseTLSCert=YES/NO
Set this to yes to make ssmtp identify itself with a certificate.

TLSCert=<file>
Specify which certificate file should be used.

TLSKey=<file>
Specify which key file should be used (can be the same as the certificate file).

TLS_CA_File=<file>
Optional file of trusted certificates for validating the server.

TLS_CA_Dir=<file>
Optional directory of trusted certificates for validating the server.