I thought I would post over RFC1123 Section 5.2.17, for anyone interested in enabling this RFC
It refers to acceptence of Address Literals, which maybe an old RFC concept, which many may consider not worthy of accepting, for various reason, such as spam, but we have never seen spam been sent this way, so for those interested and wanting to accept address literals, please see below:
SSH into server
edit /var/qmail/control/localiphost
Delete reject and input your IP address(s), you wish to accept address literals on (it may also work if you input accept, which may cover all IP addresses, but I have not tried this, as we like to define the accepyed IP address)
edit /var/qmail/control/rcpthosts
add your IP address(s) you added to localiphost
restart qmail, service smtp restart
I hope that helps a little, and below is a test I run on one of our servers
many thanks

Acceptance of address literals Mailserver accepts mail to address literals. Mailservers are technically required by RFC1123 section 5.2.17 to accept mail to domain literals (i.e. IP addresses instead of domains). This ensures backwards compatibility and can help with delivery in certain non-optimal situations, like a DNS server being down/unresponsive.
n.n.n.n | 250 ok