Follow the simple steps mentioned below.
1. Open your Outlook,
2. Opens the Visual Basic Editor (Alt+F11) and open Project-Project 1 (left side). If this doesn’t open Project-Project 1, then Press Ctrl+R.
3. On the Left Pane, you can see "Microsoft Outlook Objects" or "Project1", expand this. Now one can see the ThisOutLookSession
4. Double click on ThisOutLookSession. It will open up a Code Pane on the right hand side.
5. Copy and Paste the following code in the right pane (Code Pane) and save it
Private Sub Application_ItemSend(ByVal Item As Object, Cancel As Boolean) Dim strSubject As String strSubject = Item.Subject If Len(Trim(strSubject)) = 0 Then Prompt$ = "Subject is Empty. Are you sure you want to send the Mail?" If MsgBox(Prompt$, vbYesNo + vbQuestion + vbMsgBoxSetForeground, "Check for Subject") = vbNo Then Cancel = True End If End If End Sub
6. Now whenever you try to send a mail without subject, a pop-up is raised to remind you of the blank subject.
Please suggest better methods if you know. Please notify if it is not working for you.