[Mailman-Users] How to solve SMTP relaying denied problems

[roberto]

Dear all,
I have set up mailman and added a list of aliases into /etc/aliases and
also run the command 'newaliases'.
Then I subscribed and post message to the mailing list. But I can't get
any returned mail. I telnet and view
the /home/mailman/logs. No message in 'error' file but found some
messages in 'smtp-failures' file.
The message is like:
... TrySMTPDelivery: To xxx at yyy.com
... TrySMTPDelivery: Mailman.pythonlib.smtplib.SMTPRecipientsRefused /
{'xxx at yyy.com': (550, '<xxx at yyy.com>... Relaying denied')} (dequeued)

What should I do?
Thanks for help.

Roberto