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Question about feature "Check valid MX record on receive"

Printed From: LogSat Software
Category: Spam Filter ISP
Forum Name: Spam Filter ISP Support
Forum Description: General support for Spam Filter ISP
URL: https://www.logsat.com/spamfilter/forums/forum_posts.asp?TID=4589
Printed Date: 16 April 2025 at 12:05am


Topic: Question about feature "Check valid MX record on receive"
Posted By: Dan B
Subject: Question about feature "Check valid MX record on receive"
Date Posted: 17 November 2004 at 6:41pm

R,

Can you clear this up?

Does it lookup the domain and matches the MX from the DNS server results to the ip address connecting to SF or does it just look to see if a MX exists?

Thanks

Dan B


Replies:
Posted By: Desperado
Date Posted: 17 November 2004 at 6:55pm

Dan,

A while back, I asked the same question and received the following:

When a new connection is made, the new max IP limit is counting the number of connections form that IP currently already established in that instant. If higher than the threshold, the connection is dropped (with the appropriate error message). This prevents an IP form flooding your gateway with concurrent connecitons.
 
There are no NDR's, the connection is dropped even before they have a chance to say HELO.
 
The text is automatically added to your database in the tblRejectCodes under ID 16.
 
Does that help?
 
Regards,
Dan S.

Posted By: Dan B
Date Posted: 18 November 2004 at 2:02am

Dan,

That doesn't make sense.  I can see that pertains to the SMTP concurrent sessions, but not to the MX lookup results. Maybe Roberto was thinking of concurrent sessions while answering your question.

Thanks,
Dan B

Posted By: Desperado
Date Posted: 18 November 2004 at 8:24am

Dan,

You are correct ... I was referring to the connections.  The MX looks at the return address (or the from actually i believe) and does a MX lookup on the domain part to see if a valid entry is in dns for a good return path.  If the return is either no-existant OR if the value is 127.0.0.x, then the test fail as it should.  I actually had asked Roberto for this as we were getting a ton of undeliverable NDR's due to invalid MX records or even worse an MX that returned 127.0.0.1

Dan S.

 

Posted By: bpogue99
Date Posted: 18 November 2004 at 12:21pm

Dan,

Thanks for clearing this up as I was just about to ask the same question about the MX record. I have one customer that receives about 30,000 emails per week, but probably 28,000 are spam. The problem has been that they're a recruiting firm and have no idea where the email may be coming from, so this MX record lookup will help as the main email they are concerned about are one's where they'd have to respond, meaning there has to be a valid MX lookup to respond to it. Excellent idea, thanks to Dan S and the others for suggesting this to Roberto and the team!

bill

Posted By: LogSat
Date Posted: 18 November 2004 at 6:24pm
Dan B,

Dan S is correct. First of all we should all thank him for the idea, since the request to block emails with MX records that had loopback addresses in them was his. The side effect of his request was to be able to block all emails with, besides "naughty" MX records with values of 127.0.0.xx, also any domain (as specified in the MAIL FROM smtp command) that does not have an MX record in their DNS.

Roberto F. LogSat Software


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