[ExchangeList] Re: IMF config

  • From: "Jim Harrison" <Jim@xxxxxxxxxxxx>
  • To: <exchangelist@xxxxxxxxxxxxx>
  • Date: Fri, 2 Jun 2006 08:39:13 -0700

-------------------------------------------------------Unfortunately, that 
analogy is flawed.
RDNS isn't "validating the origin"; it's "validating the PTR records in the 
netblock owner's DNS server" and nothing else.  There are quite a few folks 
that can't get a valid PTR record built because their ISP doesn't provide such 
a simple service.
The closest thing to your analogy is an SPF TXT record.  This uses the DNS 
associated with the sending mail domain to determine the validity of the 
sending host.

Also keep in mind that unless you're the netblock owner (<giggle> as if any SBS 
deployment could be), you can build PTR records in your public DNS all day long 
and not affect remote PTR lookups in any way whatsoever.

The only functional way to work around this is via smarthost that actually does 
have a valid PTR record.

   Jim Harrison
   MCP(NT4, W2K), A+, Network+, PCG
   Read the help / books / articles!

-----Original Message-----
From: exchangelist-bounce@xxxxxxxxxxxxx 
[mailto:exchangelist-bounce@xxxxxxxxxxxxx] On Behalf Of Taylor, George
Sent: Friday, June 02, 2006 08:05
To: exchangelist@xxxxxxxxxxxxx
Subject: [ExchangeList] Re: IMF config

Hmmm, should I dance around like a god?  or do they even dance?  :-)
I have to disagree with you John.  It is standard practice to require a valid 
RDNS lookup in order to except a piece of mail.  Basically all you are doing is 
verifying that the sender is in fact who they say they are, or should I say the 
server connecting to your server is who it is advertising itself as.  As you 
say, take a look at the real world:
A guy walks into your mailroom wearing a purple shirt with a unibomber emblem 
and says "Take this package, it's from UPS..."  What's your mail clerk going to 
say?  "I'll take it because I don't care who you are, I just take all packages 
addressed to me..."?  I hope not, that's how things get blown up, that's how 
your email system will get blown up with viruses, spam, threats, etc...  If you 
cannot verify the origin of a piece of mail and you except it anyways, you put 
yourself at risk, a conscience email administrator is not going to allow that.
Just my .02
George Taylor
Systems Programmer
Regional Health Inc.


From: John T (Lists) [mailto:johnlist@xxxxxxxxxxxxxxxxxxx]
Sent: Thursday, June 01, 2006 5:07 PM
To: exchangelist@xxxxxxxxxxxxx
Subject: [ExchangeList] Re: IMF config

Andrew, please tell me you are not actually considering doing this.


Yes, the big want-to-be Internet God's such as America Off Line block/refuse on 
no PTR, but that is not practical in the real world as the rest of us know it. 
Besides, I think America Off Line is just trying to get on Dan Quails' good 
side, if he has one.


John T

eServices For You


"Seek, and ye shall find!"


-----Original Message-----
From: exchangelist-bounce@xxxxxxxxxxxxx 
[mailto:exchangelist-bounce@xxxxxxxxxxxxx] On Behalf Of Andrew English
Sent: Thursday, June 01, 2006 4:05 AM
To: exchangelist@xxxxxxxxxxxxx
Subject: [ExchangeList] Re: IMF config


Is there anyway to get IMF to drop emails that fail reverse lookup?





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