Mail issue solution query- host map: lookup (domain): deferred

UNIX Solaris
1

Hi all

I had a mail issue earlier today where I was not receiving any emails from the servers of one of our clients.
The mail queue just showed this:

-----Q-ID----- --Size-- -----Q-Time----- ------------Sender/Recipient-----------
o8S7eSpp020274*    5858 Tue Sep 28 10:42 <user@host.client.com>
                 (host map: lookup (site.co.za): deferred)
                                         <user@site.co.za>
                Total requests: 1

Looking around on Google I found a solution;
"host map: lookup (domain): deferred"

I have a query about what I changed in the /etc/mail/cf/cf/main.mc file.

I Replaced this line:

define(`confFALLBACK_SMARTHOST', `mailhost$?m.$m$.')dnl

With this line:

define(`confBIND_OPTS', `WorkAroundBrokenAAAA')dnl

as per the suggestion on that link and the mail now works.

What exactly does that line do? What is the change specifying/doing?