Hi, we have configured ubuntu server 10.04, DNS server and postfix.
We received the following answer to our e-mail sent:

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 mail system
: host mail.astivik.com.co[] said: 421 Refused. You have no reverse DNS entry. See:
http://www.your-domain-here.com/spam...D_RDNS_MISSING (in reply
to RCPT TO command)

We have checked the configuration of the reverse resolution but it seems to be ok.

What's the reason for this problem?