'Here is a quick way to have a check box on a form 
'toggle to all select or all deselected.  IN this example 
'we are updating a field in the customers table named
'Send as if we are setting the Send check box before 
'you send an email.

'On your form create a check box and name it SetAll
Dim db As Database
Dim emprevw As Single
Dim sql As String
' send all toggle check box
eprevw = Me.SetAll.Value
Set db = CurrentDb()

If eprevw = -1 Then
  sql3 = "UPDATE Customers SET Customers.Send = -1"
  db.Execute sql3
  DoCmd.Requery
Else
  sql3 = "UPDATE Customers SET Customers.Send = 0"
  db.Execute sql3
  DoCmd.Requery
End If
' The following line would update the subform "emails" on a
' master form "emailprocessor" if you put the check box on the
'master form.
Forms![emailprocessor]![Email].Form![emails].Requery