It sounds like you're asking if there's a way in real time to check to
see if your user got the message. If so, I would recommend that you
don't pursue that path. While most times email delivery seems to be
instantaneous, it could be held up for any length of time prior to
being delivered to the recipient's mailbox.
I suggest you to go through following asp.net forum links:
SMTP server and email FAQ
Delivery Notification Not Working when Sending Emails
Best Practice to do implement checking if the email sent
Note: There is no reliable way to find out if a message was indeed delivered.
There are another SO thread already availalbe that you have asked:
How to check MailMessage was delivered in .NET?
ASP.NET MVC How to determine if the e-mail didn't reach the receiver
