Please follow the instructions to setup SMTP Authentication within Outlook 2010
Once you have Outlook open go to the 'File' Tab then to the 'Info Section' and left click
'Account Settings' Left click again on 'Account Settings...'
Left click on your email account from the list and left click the 'Change...' Button
Change the 'Outgoing mail server (SMTP)' to your SMTP server e.g. mail.yourdomain.com.au
Once you have completed this left click the 'More Settings...' button
Left click the 'Outgoing Server' Tab and Tick 'My outgoing server (SMTP) requires authentication' please confirm 'Use same settings as my incoming mail server' has been selected.
Once you have completed this left click the 'OK' button You will come back to this window simply left click the 'Next' button
In the next window left click the 'Finish' button, then Left click the 'Close' Button in the Account Settings window.
Now close and and reopen outlook and you should be able to send an email.