GetCertForSignature("user@email.com")

Public Function GetCertForSignature(ByVal signature As String) As CAPICOM.Certificate
  Dim MyStore As New CAPICOM.Store
  
  ' Open the MY store and retrieve the first compartible certificate from the
  ' Store. The signing operation will only work if this
  ' certificate is valid and has access to the signer's private key.
  MyStore.Open CAPICOM_CURRENT_USER_STORE, "MY", CAPICOM_STORE_OPEN_READ_ONLY
  Dim cert As CAPICOM.Certificate
  For Each cert In MyStore.Certificates
    If cert.IsValid Then
      Debug.Print cert.SubjectName
      If (???)
        GetCertForSignature=cert
        Exit Function
      End If
    End If
  Next

End Function