OK, the fog is clearing. If you press Send and there is no recipient you will always get a warning. You can't send a message without a recipient.
Do I take it that when you have Sales Order in the Subject that you wish to check the recipients to ensure that an e-mail address is included among those recipients? In that case, put the following in the ThisOutlookSession module.
Option Explicit
Private Sub Application_ItemSend(ByVal Item As Object, Cancel As Boolean)
'Graham Mayor - http://www.gmayor.com - Last updated - 25/11/2016
Dim oRecipient As Recipient
Dim bName As Boolean
Const strAddress As String = "someone@somewhere.com" 'The address you wish to check
If InStr(1, Item.subject, "Sales Order") = 1 Then
For Each oRecipient In Item.Recipients
If oRecipient.Address = strAddress Then
bName = True
Exit For
End If
Next oRecipient
If bName = False Then
If MsgBox("The recipient '" & strAddress & "' is missing from the message." & vbCr & _
"Do you wish to send the message?", vbYesNo) = vbNo Then Cancel = True
'or just add the address e.g.
'Item.Recipients.Add(strAddress).Type = 2 'as CC (1 for To, 3 for BCC)
'Item.Recipients.ResolveAll
End If
End If
lbl_Exit:
Set oRecipient = Nothing
Exit Sub
End Sub