show hyperlink in email

Hi,
I send activation information to user in email.
I send web address to user  Like, www.mywebsitename.com 
But  when i place mouse over it, i am not able to click it.  though i can see underline & changed font color (blue) but I am not able to click it in yahoo.
I want, when user place mouse over it, mouse cursor should detect is hyperlink & should be able to click & navigate.

here is my code:
    Dim sbBody As New StringBuilder()
 message.IsBodyHtml = "true"
sbBody.Append("<html><body>")
sbBody.Append("<a>www.mywebsite.com</a>")

 
 
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