Impossible envoyer message sur outlook express

Bonjour,
J'essaie depuis 1 semaine de faire parvenir un message à un correspondant irlandais, voici le retour que je reçois :

From: "Mail Delivery System" <MAILER-DAEMON@smtp1-g19.free.fr>
To: <isabelle.xxxxxx@free.fr>
Sent: Monday, May 26, 2008 11:54 PM
Subject: Undelivered Mail Returned to Sender


> This is the Postfix program at host smtp1-g19.free.fr.
>
> I'm sorry to have to inform you that your message could not
> be delivered to one or more recipients. It's attached below.
>
> For further assistance, please send mail to <postmaster>
>
> If you do so, please include this problem report. You can
> delete your own text from the attached returned message.
>
> The Postfix program
>
> <xxxxxxx@2fm.ie>: host maillist2.rte.ie[89.207.56.93] said: 550
>    <xxxxxxxx@2fm.ie>: Recipient address rejected: User unknown in
> virtual
>    alias table (in reply to RCPT TO command)

Avez vous une solution à m'apporter ????

Je vous remercie par avance de votre aide