Function ValidAddr(addr As String) As Boolean
    Dim BadAddrs(2)
    Dim pos As Long
    Dim i As Integer
    pos = 0
    i = 0

    BadAddrs(0) = "PO BOX"
    BadAddrs(1) = "P.O BOX"
    BadAddrs(2) = " P.O. BOX"
    
    For i = LBound(BadAddrs) To UBound(BadAddrs)
        If (pos = 0) Then
            pos = InStr(1, addr, BadAddrs(i))
        End If
    Next i
    
    If (pos <> 0) Then
        ValidAddr = False
    Else
        ValidAddr = True
    End If
End Function

Sub CheckAddr()
    Dim isAddrPOBox As Boolean
    isAddrPOBox = False
    
    isAddrPOBox = ValidAddr("P.O BOX Rt. 11 P.O there")
    MsgBox isAddrPOBox
End Sub