Here's some sample VBA code using Outlook Redemption that Huseyint found.
Public Sub ProcessMail()
Dim Sess As RDOSession
Dim myMsg As RDOMail
Dim myString As String
Set Sess = CreateObject("Redemption.RDOSession")
Set myMsg = Sess.GetMessageFromMsgFile("C:\TestHarness\kmail.msg")
myString = myMsg.Body
myMsg.Body = Replace(myString, "8750", "XXXX")
myMsg.Save
End Sub