Only run code on a checked box?

Hi is there a way to only run code in vba on a checked box (ActiveX)

I have this.....

Private Sub CheckBox1_Click()
Dim OutlookApp As Object
Dim Mess As Object, Recip
Recip = [L7].Value
Set OutlookApp = CreateObject("Outlook.Application")
Set Mess = OutlookApp.CreateItem(olMailItem)
With Mess
.Subject = "Task Completed"
.Body = "XXXXXX XXXXXX has completed task" & " " & Range("C7").Value
.To = Recip
.Display
.Send
End With
End Sub

But it runs when i check and uncheck the box, i dont want it to anything when i uncheck it, and have tried

If checkbox value = !xon then cell = and also used a Change_Event for a cell so that it Calls a macro, and still cant get it to work only on a checked box.

Any help?

Dan