SMTP questions

[Justin Zygmont]

I just had a few questions about SMTP,

SMTP AUTH with saslauthd will encrypt the username/password but not the rest of 
the message being transmitted correct?

STARTTLS will encrypt the entire data transmission, including the message also, 
right?

It just makes me wonder what difference there would have to be configured from 
the client side to make use of: saslauthd authentication, SSL, or starttls. 
All I remember seeing from the client side was something like: "use secure 
authentication" but nothing to differentiate between which kind of secure SMTP.