I got the code from below blog/fourm:
How to Get a Notification If Not Receiving the Reply of a Specific Email within Expected Time - Data Recovery Blog
Public WithEvents objInboxItems As Outlook.Items
Private Sub Application_Startup()
Set objInboxItems = Application.Session.GetDefaultFolder(olFolderInbox).Items
End Sub
'If receive the reply, clear the flag and remove the reminder
Private Sub objInboxItems_ItemAdd(ByVal Item As Object)
Dim objSentItems As Outlook.Items
Dim objVariant As Variant
Dim i As Long
Dim strSubject As String
Dim dSendTime As String
Set objSentItems = Outlook.Application.Session.GetDefaultFolder(olFolderSentMail).Items
If Item.Class = olMail Then
For i = 1 To objSentItems.Count
If objSentItems.Item(i).Class = olMail Then
Set objVariant = objSentItems.Item(i)
strSubject = LCase(objVariant.Subject)
dSendTime = objVariant.SentOn
If LCase(Item.Subject) = "re: " & strSubject Or InStr(LCase(Item.Subject), strSubject) > 0 Then
If Item.SentOn > dSendTime Then
With objVariant
.ClearTaskFlag
.ReminderSet = False
.Save
End With
End If
End If
End If
Next i
End If
End Sub
'Get a prompt asking if to send a notification email
Private Sub Application_Reminder(ByVal Item As Object)
Dim strPrompt As String
Dim nResponse As Integer
Dim objFollowUpMail As Outlook.MailItem
'You can change the subject as per your real case
If (Item.Class = olMail) And (LCase(Item.Subject) = "datanumen outlook repair") Then
strPrompt = "You haven't yet recieved the reply of " & Chr(34) & Item.Subject & Chr(34) & " within your expected time. Do you want to send a follow-up notification email?"
nResponse = MsgBox(strPrompt, vbYesNo + vbQuestion, "Confirm to Send a Follow-Up Notification Email")
If nResponse = vbYes Then
Set objFollowUpMail = Application.CreateItem(olMailItem)
With objFollowUpMail
.To = Item.Recipients.Item(1).Address
.Subject = "Follow Up: " & Chr(34) & Item.Subject & Chr(34)
.Body = "Please respond to my email " & Chr(34) & Item.Subject & Chr(34) & "as soon as possible"
.attachments.Add Item
.Display
End With
End If
End If
End Sub
