Mail goes to spam/junk folder (using System.Net.mail)

Hello Friends,
I am sending mail from my application using System.Net.Mail i.e. MailMessage.
Mails are sending successfully, but It goes to spam/junk mail folder of the receiver. It is not consistent for all receiver addresses. In Yahoo it goes to Inbox folder, and for Gmail & Hotmail it goes to spam/junk folder.
I have read many posts regarding same issue. It says it is indepenent how we send mails. But I want to resolve this issue for my application.
I am using mailsettings of web.config file and specified the required credentials for sending mails.
Thanks
Chital
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