As of January 2011, due to changes in their services, the ISP (Internet Service Provider) Orange no longer permit customers to use 3rd party outgoing mail servers (smtp).
If you are using Orange's internet connection, you will now need to use their smtp as your outgoing mail server smtp.orangehome.co.uk in order to send email.
For further information, please see Orange's support article:
http://help.orange.co.uk/orangeuk/support/personal/233487.