This is the Postfix program at host smtp6-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
<firstname.lastname@example.org>: host mx1.free.fr[220.127.116.11] said: 550 5.1.1 user
unknown (in reply to RCPT TO command)
D'avance MERCI pour votre aide