In that case you can assign the categories with a macro and reply accordingly e.g. as follows. Change the categories and the texts as required.
Option Explicit
Sub CategorizeAndReply()
Dim objMail As MailItem
Dim olItem As MailItem
Dim olInsp As Inspector
Dim wdDoc As Object
Dim oRng As Object
On Error Resume Next
Select Case Outlook.Application.ActiveWindow.Class
Case olInspector
Set objMail = ActiveInspector.currentItem
Case olExplorer
Set objMail = Application.ActiveExplorer.Selection.Item(1)
End Select
objMail.ShowCategoriesDialog
If Not objMail.Categories = "" Then
Set olItem = objMail.Reply
With olItem
.BodyFormat = olFormatHTML
Set olInsp = .GetInspector
Set wdDoc = olInsp.WordEditor
Set oRng = wdDoc.Range(0, 0)
.Display
Select Case objMail.Categories
Case "Category name 1"
oRng.Text = "This is the message for Category name 1" & vbcr & vbcr & "More message text" 'etc
Case "Category name 2"
oRng.Text = "This is the message for Category name 2"
Case "Category name 3"
oRng.Text = "This is the message for Category name 3"
Case "Category name 4"
oRng.Text = "This is the message for Category name 4"
'etc
End Select
'.Send
End With
Else
Beep
MsgBox "No category assigned"
End If
lbl_Exit:
Set objMail = Nothing
Set olItem = Nothing
Exit Sub
End Sub