Rule that runs macro when an email is opened

Question

I have created a macro, that does certain things, to an opened mail. I would like to create a rule, that does it automatically, when I open the mail.

I don't want this rule to run all time, just when I open a mail, I don't want to force this rule on each mail I receive.

Answer 1

Following @ZZA comments,

try this code:

Public WithEvents myItem As Outlook.MailItem

Private Sub Application_ItemLoad(ByVal Item As Object)
    If Item.Class = olMail Then
        Set myItem = Item
    End If
End Sub


Private Sub myItem_Open(Cancel As Boolean)

   'Your code
End Sub

Paste code in ThisOutlookSession

EDIT

To avoid 'Your code triggering the event we need an event disabler:

Public WithEvents myItem As Outlook.MailItem
Public EventsDisable as Boolean

Private Sub Application_ItemLoad(ByVal Item As Object)
    If EventsDisable = True Then Exit Sub
    If Item.Class = olMail Then
        Set myItem = Item
    End If
End Sub


Private Sub myItem_Open(Cancel As Boolean)
    EventsDisable=True
   'Your code
    EventsDisable=False
End Sub