For testing perhaps try switching the To and Cc parts to see if e-mails are really being sent. If e-mails are being sent then perhaps yahoo is flagging your e-mail as spam for some reason. If e-mails are not being sent then perhaps switch to the newer CDO instead of the outdated CDONTS.
I am running win server 2003 and CDONTS still works with it.
if the company you are using for hostnig is set up like me, then the email address that you are putting in the "from" part of the message has to exist on the server. otherwise the server just rejects the attempt and it goes into digital oblivion. its a measure to help prevent spam. it requires that the sender of the email have a valid account on the server.
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