How to call public function

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VB

Hi, I have a public function to call default email client.

Public Function OpenEmail(ByVal EmailAddress As String, Optional ByVal Subject As String = "", Optional ByVal Body As String = "") As Boolean
       Dim bAns As Boolean = True
       Dim sParams As String
       sParams = EmailAddress
       If LCase(Strings.Left(sParams, 7)) <> "mailto:" Then _
           sParams = "mailto:" & sParams

       If Subject <> "" Then sParams = sParams & _
             "?subject=" & Subject

       If Body <> "" Then
           sParams = sParams & IIf(Subject = "", "?", "&")
           sParams = sParams & "body=" & Body
       End If
   End Function

Then in Button_click, I put

<pre lang="vb"> OpenEmail("mail@asdf.com", "Subject", Body:=" of my message")

But I am unable to call the function. I want to open the client when I click button1
Thanks