Problems sending email with Outlook 2007

[davyeon]

Hi,

I am trying to send emails using outlook 2007 and i'm receiving the following errors. It seems to be a desktop issue seeing that i can send emails via my BB and other applications but not using outlook.

Your message did not reach some or all of the intended recipients.

Subject: RE: dev.athletixnation.com
Sent: 8/19/2007 10:01 PM

The following recipient(s) could not be reached:

'Bobby Williams' on 8/19/2007 10:01 PM
554 5.7.1 <bobby.williams@iastar.net>: Relay access denied

Any assistance would be appreciated.

Thanks

[edge]

Make sure that you set My server requires authentication to ON in Outlook.

[davyeon]

My server requires authentication is already set.

Any other thoughts?

Thanks
dr

[falko]

What's in /etc/postfix/main.cf (please strip out the comments)?
What's the output of telnet localhost 25 and then ehlo localhost?

Any errors in your mail log?