SMTP Authentication is Required for ASP.NET
Dear Sir,
Your sender of the Email address must be an email address that is hosted on our Server. Our Email servers requires SMTP authentication. You will not be able to send emails with a sender address of (someone@yahoo.com), as the sender of the Email because we are not hosting (someone@yahoo.com at our servers. Our Email servers does not send emails on behalf of any email address that is not hosted on our server. Here is what you should do.
Since you are using ASP.Net, in your web.config file please ensure that you provide the following information correctly. See the XML code below,
USERNAME@YourDomain.com -- This should be a correct email address that is at your domain.
EMAIL_PASSWORD_HERE -- This should be the correct password of the above email address.Then, when you send the email, the sender of the email must also be USERNAME@YourDomain.com. The sender of the email must match the email address that you are using for SMTP Authentication.
<system.net>
<mailSettings>
<smtp>
<network host="SMTP.YourDomain.com" userName="USERNAME@YourDomain.com" password="EMAIL_PASSWORD_HERE" />
</smtp>
</mailSettings>
</system.net>Please visit the follow Website for detailed information on:
Sending Email in ASP.NET 2.0 with SMTP Authentication
http://www.4guysfromrolla.com/articles/072606-1.aspx