hostname does not resolve to address

==== Required information ====
- iRedMail version: iRedMail-0.8.4
- Store mail accounts in which backend (LDAP/MySQL/PGSQL): Mysql
- Linux/BSD distribution name and version: Debian 7.2
====

Hello Zhang,

You have suggested me that the hostname and First Virtual Domain Name should be different.

So I gave hostname as 'mx.mydomain.org' and the First Virtual Domain Name as 'mydomain.org', so that I can create email ids like myname@mydomain.org. This works totally fine.

Now I tried to send an email from mydomain.org to another server, which also runs iRedmail. When I looked at the /var/log/mail.log of the destination server, I found the following:

Jun 30 07:05:38 server postfix/smtpd[4259]: warning: hostname mx.mydomain.org does not resolve to address 128.129.62.124: No address associated with hostname

Is this a related issue ? How can I resolve this ?

Thanks.