That's a relay error generated by your server. You're IP address is not allowed to send through it unless you authenticate probably.
Check the docs again there's info on that issue in there (although offhand I can't remember where exactly - search the help file for relaying). Also on teh West Wind Wiki.
http://www.west-wind.com/wiki/Specifically:
http://www.west-wind.com/wiki/kb.wiki?wc~EmailRelayingDenied572+++ Rick ---
>I am trying to send email and I get
>
>Error 550 Unknown user
>
>however the Joel@qtss.com is the recepient and not the sender and I should be able to use any recepient address.
>
>o=CREATEOBJECT('wwIPStuff')
> o.cMailServer='pearland.com'
> o.cSenderEmail='joel@Pearland.com'
> o.cpassword="frances"
> o.cSenderName='Test '
> o.cRecipient="Joel@qtss.com"
> o.cSubject='Your new Seaport Museum Login ID'
> o.cMessage='Thank you '
>
>llResult = o.SendMail()
>
>IF !llResult
> Wait window o.cErrorMsg timeout 10
>ELSE
> WAIT wind "Email sent " timeout 2
>ENDIF
