There is certainly nothing there to override the earlier RFC (which I've forgotten) that specifies a similar recommendation but goes on to say that the receiver MUST NOT reject the message based on an address lookup mismatch for the HELO/EHLO name (obviously written by someone who realized that multi-homed servers are common and that corporate servers often live behind NAT firewalls and don't even know the address that will be used the public side).

-- Les Mikesell les@futuresource.com

I believe you are referring to RFC 821:

The HELO receiver MAY verify that the HELO parameter really corresponds to the IP address of the sender. However, the receiver MUST NOT refuse to accept a message, even if the sender's HELO command fails verification.