questo č l'errore... come posso risolvere?

This is the Postfix program at host webserver.maydomain.it.

I\'m sorry to have to inform you that your message could not be
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

<name@mailcity.it>: host pop.mailcity.it[62.94.184.226] said: 553 sorry,
your
envelope sender domain must exist (#5.7.1) (in reply to MAIL FROM
command)