Why email not being sent

I have this code in the afterupdate event of a checkbox.  But when the checkbox is checked true the email is not being sent.  In fact nothing is happening.

Private Sub chkbxSampleShipped_AfterUpdate()

   If Me.chkbxSampleShipped = True Then
   
Dim varName As Variant
Dim varCC As Variant
Dim varSubject As Variant

    varName = "somebody@somewhere.com"
    varCC = "somebodyelse@somewhere.com"

    varSubject = "The sample has been shipped for part # - " & [txtPartN] & ""

    DoCmd.SendObject , , , varName, varCC, , varSubject, varBody, True, False
   
    MsgBox "The samples shipped notification has been emailed to Bill and Bob."

    End If

End Sub

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