Changing email display name

Hi
I am using a vb.net application to send emails, the account I am using is for example:
test@test.com
the email name is: test name
I need to send the email with changing the name of the sender like
"My Name" instead of "test name"
my code is:
Dim msgMail As MailMessage

Dim Sendername as string = "My Name"
msgMail.From = Sendername & "<test@test.com>"
it was working OK with my exchange server but now it doesn't I really dont know why????!!!

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