Ah, OK. That's unlike EE's Port 587 SMTP which will send from any email addy as long as you authenticate it with your own email addy. Are you sure that's not sufficient?
1999: Freeserve 48K Dial-Up => 2005: Wanadoo 1 Meg BB => 2007: Orange 2 Meg BB => 2008: Orange 8 Meg LLU => 2010: Orange 16 Meg LLU => 2011: Orange 20 Meg WBC