SMTP Relay Error using CDONTS and the .CC property in ASP

Hey, this is a real head scratcher.

The following code works as written:

Set objMail = CreateObject("CDONTS.NewMail")
objMail.From = "test@insidedomain.com"
objMail.To = "test@outsidedomain.com"
objMail.Subject = "SMTP TEST"
objMail.Body = "TESTING"
objMail.Send
Set objMail = Nothing

However if I add the the following code after the .To statement:
objMail.CC = "test@insidedomain.com"

What happens is that the mail gets delivered to the .CC address but a
relay error occurs on the .To address.

Once I take out the .CC statement, the .To address gets the delivery.

Any ideas?

Thanks.

Here is the nondeliverable mail bounce back:

Connection to mail.xxxxx.com with Ip Address 10.1.3.11 failed from
mimesweeper.xxxxx.com-10.1.3.11
test DeleteThis @outsidedomain.com
550 Relaying denied to <test DeleteThis @outsidedomain.com>

And the entry in the system32/logfiles/smtpsvc1 log file is:

NDR Thread NDR message
user+test@outsidedomain.com+in+file+filename.eml+was+NDRed+to+file+filename.eml
0

Thanks!