Hi Natalie,
Right, If your SMTP domain zone is not stored in your internal DNS, it is not necessary to add an internal autodiscover record - the one in your external (public) DNS is sufficient.
Did you configure Outlook using the Desktop Setup Application, per me and Youngs advise? onlinehelp.microsoft.com/.../ff637537.aspx (Resources\Download in your portal).
Best regards,
Jesper Ståhle