problemi con l'invio della posta

["Giulio F." <gf77p@inwind.it>]

Ciao,
Quando invio la posta exim mi da quest'errore, a cosa potrebbe essere dov=
uto?

This message was created automatically by mail delivery software (Exim).

A message that you sent could not be delivered to one or more of its
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  giuliof@inwind.it
    SMTP error from remote mailer after MAIL FROM:<giulio@debian> SIZE=3D=
1513:
    host mail.inwind.it [193.70.192.50]: 553 <giulio@debian> Invalid mail=
=20
address,=20
    must be fully qualified domain

Grazie x le risposte
Ciao
Giulio F.