As a Wanadoo.fr subscriber I can tell you that there seem to be two separate problems:
1. Messages from a Wanadoo.fr address are blocked by SORBs if sent to at least six different ISPs, not so far including ntlworld in my experience. Sorbs tells me that this is due to Wanadoo.fr allowing spammers to use Wanadoo addresses for sending out their daily effusions, and that until Wanadoo.fr gets its house in order I can whistle for the chance to correspond with my friends at these six (and more every week) ISPs. I have written to
service.clients@wanadoo.fr about 15 times about this, and have never received a sniff of a reply.
As it is illegal to send spam in France, maybe they are worried about being prosecuted for allowing spammers to use their services . . . . ?
2. Messages sent from my wanadoo.fr address to ntlworld addresses (and four other known ISPs so far) are simply bounced with an "End of Data" error message, and a suggestion that I write to
Postmaster@wanadoo.fr about this for an explanation. Which I have done at least a dozen times with no reply from Wanadoo.fr whatsoever.
It appears to me that Wanadoo.fr don't care a tuppeny whatsit for their customers, and as soon as I can work out some way of leaving them to their own devices (?) I shall do so.