require_rdns.m4 (Was Require RDNS?)

Jeff A. Earickson jaearick at
Thu Aug 17 21:27:38 IST 2006

On Thu, 17 Aug 2006, Steve Freegard wrote:

> Date: Thu, 17 Aug 2006 20:46:33 +0100
> From: Steve Freegard <steve.freegard at>
> Reply-To: MailScanner discussion <mailscanner at>
> To: MailScanner discussion <mailscanner at>
> Subject: Re: require_rdns.m4 (Was Require RDNS?)
> Hi Jeff,
> Jeff A. Earickson wrote:
>> Gang,
>> I rolled out require_rdns.m4 this morning and my phone is starting
>> to ring.  I have discovered that our network guy created (at least)
>> two entire subnets in DHCP but never bothered to create DNS zones
>> for them, so I have whole chunks of my campus not able to send email!
>> My question for you sendmail mc gurus:  instead of doing
>> $#error $@ 5.7.1 $: 550 RDNS: Fix reverse DNS for $1
>> in require_rdns.m4, I want to just log the message and go on (dry-run
>> mode), something like:
>> $#print $@ 5.7.1 $: 550 RDNS: Fix reverse DNS for $1
>> Anybody know how to tweak an mc to just syslog an action?
> I'm not sure how to do that -- but you could 'whitelist' your internal IP 
> address ranges using the access.db if you have the latest version of the hack 
> (see: - e.g.
> rdns:192.168.47		OK
> Just a thought.

Excellent point, I missed that.  However Da Boss asks "Can we try this
in dry-run mode?  Just log what rdns would do, but not really do it?"
She has a good point.  My ability to decipher files has
always been weak.  I thought about changing the $#error numbers to 200,
but figured that would blow up.

Billy, I take responsibility for my own stupidity.  You didn't force
me to retry RDNS today...

Jeff Earickson
Colby College

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