ssmtp configuration for server authorization

[perrin at apotheon.com]

I seem to be having some authorization problems with an SMTP server using
ssmtp.  I want to make sure the configuration is correct before I blame the
problem on something else (like the company that runs the server).

In the following ssmtp.conf file contents, assume these values for anything
to the right of an equals sign:

"user" is the mail account name
"domain" is the domain for the SMTP server
"password" is my password for the "user" mail account
"laptop" is the hostname of my laptop, where I'm running ssmtp
"local" is the local network name
"mail" is the hostname of the SMTP server (and mail.domain.org is the FQDN)

This is my ssmtp.conf:

  root=user at domain.org

  mailhub=mail.domain.org

  AuthUser=user at domain.org
  AuthPass=password

  rewriteDomain=domain.org

  hostname=laptop.local

  FromLineOverride=YES

Is something missing or mis-specified?  Did I misunderstand the purpose of
one of those variables?  Are some of those unusable with the FreeBSD version
of ssmtp?  Is there something else I should be doing for authorization on
the SMTP server?  Is something in the wrong order?

Note that on the SMTP server the complete login name for that mail account
is "user at domain.org", not just "user", according to the people managing the
server.