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From: Miles Fidelman (mfidelmanmeetinghouse.net)
Date: Sat Apr 05 2014 - 12:56:46 CDT
> On Sat, Apr 05, 2014 at 11:01:54AM -0400, Miles Fidelman wrote:
>> Which leads to several obvious questions:
>> - how does postfix use PTR records (e.g., which header lines
>> are matched, at what points in the processing chain, ...)?
> A client connects to smtpd. The PTR for the client IP address is
> looked up. The PTR value (that is, a hostname, such as
> "x.example.com.") is also looked up. If an A record matching the
> client IP address is returned, smtpd logs the connection as coming
> from "x.example.com[client.ip.add.ress]". Then if mail is eventually
> accepted, the Received header is constructed similarly:
> Received: from <helo_name_given> (x.example.com[client.ip.add.ress])
Well... it's a little more complicated than that:
- there's the initial TCP connection - where there are only IP addresses
and port numbers involved
- there's the HELO command - HELO name is given
- then there's the MAIL command - where you have the sender email
address (which may be a different domain from the HELO domain)
And a bunch of other things are logged (depending on logging
- envelope from: and to:
- from: and to: addresses from the message body
- alias translations (e.g., an "originally-to: header)
> If this verification process fails, such as when no PTR exists for
> the address (see reject_unknown_reverse_client_hostname) or when the
> PTR value lookup fails (nxdomain, servfail, timeout) or returns a
> different IP address (see reject_unknown_client_hostname), smtpd logs
> the connection as coming from "unknown[client.ip.add.ress]".
> "Which header lines are matched"? I have no idea what you mean.
Well, let's start with:
- HELO name
- MAIL FROM:
Since this is a postfix list - specifically, does postfix do any
matching beyond the IP address in the TCP connection, and the PTR from
the HELO name?
In theory, there is no difference between theory and practice.
In practice, there is. .... Yogi Berra