Re: [Asrg] What are the IPs that sends mail for a domain?

Dotzero <> Wed, 17 June 2009 12:25 UTC

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Date: Wed, 17 Jun 2009 08:25:28 -0400
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Subject: Re: [Asrg] What are the IPs that sends mail for a domain?
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On Tue, Jun 16, 2009 at 6:20 PM, Franck Martin<> wrote:
> I recently encountered the following question/problems.
> I have a mail server and one of my users complains he is not receiving
> emails from a domain. How do I find if I have blocked the domain from
> sending to my server. Meaning, knowing the domain name of the sender, how do
> I find the IPs from where the mail could be sent from. It seems that SPF is
> the only tool to provide that answer?

One approach that might help you is to go to (from
ReturnPath). Register for a free account and then enter in the domain
name. For example, when I enter in it shows me that there
is one IP address sending mail for that domain - with a
hostname of

Hope this helps.

> In another related problem, which is linked to IPv6 and RBL. Buidling an
> IPv6 RBL could lead to a huge database. Sure you can alleviate by using
> "wildcards", but why not use the reverse DNS resolution to add a TXT record
> associated to the IP to indicate the IP is the one of a mail server? So any
> IP that does not have this record would be blocked for SMTP. As IPv6 is not
> used for SMTP (or barely), this could be made mandatory for IPv6 and
> optional for IPv4. An MUA could talk to an MTA on port 25 because we know
> the the etwork range of the MUA or the alternative is to use the new mail
> submit port.
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