I used Ron de Bruin's code from his site http://www.rondebruin.nl/cdo.htm

However, when I run it I get this error

The "SendUsing" configuration value is invalid.

Am I missing a reference maybe? Below is the code.

Sub submitclick()
Dim iMsg As Object
Dim iConf As Object
Dim wb As Workbook
Dim WBname As String
' Dim Flds As Variant

Application.ScreenUpdating = False
Set wb = ActiveWorkbook

' It will save a copy of the file in C:/ with a Date and Time stamp
WBname = wb.Name & " " & Format(Now, "dd-mm-yy h-mm-ss") & ".xls"
wb.SaveCopyAs "C:/" & WBname


Set iMsg = CreateObject("CDO.Message")
Set iConf = CreateObject("CDO.Configuration")

' iConf.Load -1 ' CDO Source Defaults
' Set Flds = iConf.Fields
' With Flds
'
..Item("http://schemas.microsoft.com/cdo/configuration/sendusing") = 2
'
..Item("http://schemas.microsoft.com/cdo/configuration/smtpserver") = "Fill in
your SMTP server here"
'
..Item("http://schemas.microsoft.com/cdo/configuration/smtpserverport") = 25
' .Update
' End With

With iMsg
Set .Configuration = iConf
.To = "
' .CC = ""
' .BCC = ""
' .From = """"" "
.Subject = "Out of Office Request"
' .TextBody = "This is the body text"
.AddAttachment "C:/" & WBname
.Send
End With

'If you not want to delete the file you send delete this line
Kill "C:/" & WBname

Set iMsg = Nothing
Set iConf = Nothing
Set wb = Nothing
Application.ScreenUpdating = True
End Sub