Outlook Express - error 554

[SB118]

Friend is suddenly having trouble sending emails, been fine until a few days ago, now she gets this ...

The message could not be sent because one of the recipients was rejected by the server. The rejected e-mail address was '[email protected]'. Subject 'test5', Account: 'pop.wanadoo.co.uk', Server: 'smtp.wanadoo.co.uk', Protocol: SMTP, Server Response: '554 <[email protected]>: Recipient address rejected: Access denied', Port: 25, Secure(SSL): No, Server Error: 554, Error Number: 0x800CCC79

None of the settings have changed, she using her isp mail account (which works fine if you login to the webmail system)

I put my freeserve details in the and mine was blocked too, so i'm guessing it's something OE based??

anybody?

cheers