Custom actions are .dll components built with Extended MAPI and C++ or Delphi in such a way that they can be invoked by Rules Wizard. See
http://www.slipstick.com/addins/custom.htm for code samples and commercial actions.
If you are using Outlook 2002 or later, you can create a rule with a "run a script" action that invokes not a "script" but a public VBA subroutine with a MailItem or MeetingItem argument, e.g.
A "run a script" rule action actually uses not an external script but a VBA procedure with a MailItem or MeetingItem as its parameter. That item is processed by the code:
Sub RunAScriptRuleRoutine(MyMail As MailItem)
Dim strID As String
Dim olNS As Outlook.NameSpace
Dim msg As Outlook.MailItem
strID = MyMail.EntryID
Set olNS = Application.GetNamespace("MAPI")
Set msg = olNS.GetItemFromID(strID)
' do stuff with msg, e.g.
msg.SaveAs "C:\Emails\" & msg.Subject & " " & _
Time & ".msg"
Set msg = Nothing
Set olNS = Nothing
End Sub
See
http://www.outlookcode.com/d/code/zaphtml.htm#ol2002 for another example.
--
Sue Mosher, Outlook MVP
Author of Configuring Microsoft Outlook 2003
and Microsoft Outlook Programming - Jumpstart for
Administrators, Power Users, and Developers