Question about feature "Check valid MX record on receive" |
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Dan B 
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Joined: 09 February 2005 Location: United States Status: Offline Points: 105 |
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 Topic: Question about feature "Check valid MX record on receive"Posted: 17 November 2004 at 6:41pm |
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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 |
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Desperado
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Joined: 27 January 2005 Location: United States Status: Offline Points: 1143 |
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Posted: 17 November 2004 at 6:55pm |
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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.
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Dan B
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Joined: 09 February 2005 Location: United States Status: Offline Points: 105 |
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Posted: 18 November 2004 at 2:02am |
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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, |
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Desperado
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Posted: 18 November 2004 at 8:24am |
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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.
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bpogue99
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Joined: 26 January 2005 Status: Offline Points: 59 |
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Posted: 18 November 2004 at 12:21pm |
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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 |
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LogSat
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Joined: 25 January 2005 Location: United States Status: Offline Points: 4104 |
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Posted: 18 November 2004 at 6:24pm |
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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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