Open OE, goto Tools-Accounts, then highlight your email provider. Click on Properties. Another window pops up, click on Servers Tab, in there, it will tell you what your in-coming and out-going mail servers are.
If it's "SMTP.WANADOO.COM", it's wrong. It should be your ISP provider. Like SMTP.BT.COM, something like that.
At a guess, you are still trying to send on the Wanadoo account. Wanadoo wont let you as you have cancled your account with them.