Checking for a non resolvable HELO will get you significant fps. There are plenty of HELO patterns that can and must be filtered but not this one. On Wednesday, May 8, 2013, Robert Drake wrote:

Sorry for the noise, but I thought this might be of interest to anyone waiting for their hotel confirmation:

NOQUEUE: reject: RCPT from feport01.hiltonhhonors.net[63.**122.201.171]: 450 4.7.1 <ironport.hhonorscrm.net>: Helo command rejected: Host not found; from=<waldorfastoriahotels&resorts@res.hilton.com> to=<excised> proto=ESMTP helo=<ironport.hhonorscrm.net>

So if you run your own server and/or are capable of compensating for a misconfigured MTA, you should add an exception for feport01.hiltonhhonors.net.

-- --srs (iPad)