In continuation to the question i posted earlier on stackoverflow, we would like to configure IIS of dedicated hosting server to send thousands of email. What I would like to know is, how to configure SMTP of IIS and DNS settings so that the emails sent from our asp.net application are not marked as SPAM.
You will need a proper SMTP server like Exchange or SmarterMail to send "thousands of email" successfully, you should not be relying on IIS for this.
Whether or not your emails are marked as spam has very little to do with IIS and DNS. You can setup your DNS so that you have valid reverse DNS, that your mail server is responding to helo's with the same name as its A record and you could setup a valid SPF record.
The main reason your email would be marked as spam is its content, and any blacklisting your domain or IP has. If your emails contain keywords or content that will be picked up by spam detectors, it will be marked as spam. If your on any blacklist, you will be marked as spam. To be honest, if your sending out thousands of emails, its quite probable some people will not like this and will report you as sending spam anyway, which is likely to get you blacklisted. If your content is valid and your users are expecting (or at least signed up for) your email you should have little problem with spam.
If you are infact sending spam, then you will be detected as spam, and thats the way it should be.
To configure SMTP in IIS, see following:
To prevent from SPAM, there must be valid sender(From) address in the code.