Simple, the
Credentials
[
^] property of the
SmtpClient
[
^] object is used for authentication process on the SMTP server, it is your username/password used by the SMTP client, server or other application using which you can authenticate yourself to use the service.
The
From
[
^] field in the
MailMessage
[
^] object is used in your email message, it is the field that you see in the Email messages' From field. They are (and they can be) different, but sometimes the SMTP server would notify the recipient that the email has not been sent by the From address.
Please read the attached MSDN documentations for the resources, they would clarify the requirement and fields a little bit more.