After the "530" error code, should be a short blurb on what must be
accomplished in order to send messages.  Now if I was to take a guess, the
error code could mean that in order to send messages, Outlook has to
authenticate first.  If I'm on the right track, keep reading.

If you have any type of security product installed (e.g. antivirus,
antispam, personal firewall, .etc) that can scan *outgoing* e-mail, you need
to uninstall/reinstall your security product w/out this feature enabled.
The reason why is that these programs act as a middle man between Outlook
and the mail server and generally do not support SMTP servers that require
authentication.

/neo