SMTP Deferred because of Reverse Lookup Errors

Question

When sending emails I get about 5 out of 3000 emails that are status deferred because the PTR look failed according to the SMTP response of the receiving server.

My PTR records are in order and match my EHLO.

Can anyone else who sends a good amount of email that also have a valid PTR and HELO check there logs and see what percentage of this they get?

I am wondering if I should I be looking into our reverse DNS which is currently hosted by our provider.

score 1 · Answer 1 · answered Dec 17 '10 at 15:06

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Checking your rDNS is a good idea but I would wonder if it's a DNS problem on the recipient servers, maybe they're having a problem looking up the rDNS, even though your records are in order.

answered Dec 17 '10 at 15:06

joeqwerty

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My guess is the other ends as well. That is why I am wondering if anyone has any data points on this. – Kyle Brandt Dec 17 '10 at 15:07

score 1 · Answer 2 · answered Dec 17 '10 at 15:16

I manage mail servers for about 30ish SMB customers and I see about a half dozen or so of these every month. They're pretty consistent on which domains give me the delays so I've always gone with the assumption that the problem is on the other end. Our total mail volume monthly averages about 8k with dips down to about 6k and peaks upwards of 12k. We manage everything from GroupWise, Exchange, Lotus notes, to small mail packages like MDaemon and Visnetic.

score 0 · Answer 3 · answered Dec 17 '10 at 15:22

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Have a look from different DNS servers (try 4.2.2.2). Make sure that it's not just the ehlo but also the A record that matches forward and reverse.

You might also consider setting up SPF records: http://www.openspf.org/Introduction

answered Dec 17 '10 at 15:22

Glen M

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SMTP Deferred because of Reverse Lookup Errors

3 Answers3