Categorizing emails based on the subject

[gmayor]

Is the With Events line at the top of the ThisOutlookSession module (before the macros, but after Option Explicit if present)?

e.g.

Option Explicit

Private WithEvents Items As Outlook.Items

Private Sub Application_Startup()
    Dim olApp As Outlook.Application
    'etc

as for the attachments you will need to loop through the attachments collection e.g.

For i = 1 To olItem.Attachments.Count
    If InStr(1, olItem.Attachments(i).fileName, "[CAT1]", vbTextCompare) > 0 Then
        olItem.Categories = "CAT1"
        olItem.Save
        Exit For
    End If
Next i