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Re: outgoing SMTP and dynamic DNS

bruce@va.debian.org writes:

> Few sites will accept mail any longer if they can not resolve your DNS
> reverse lookup to match your forward DNS. Most have PARANOID enabled
> in tcpd. The only ways I can see to configure outgoing mail on a
> dynamic IP system are:

I'm not really an expert on this.  I can see that tcpd gets the IP
address from the initial connection, but where does it get the name it
uses to reverse resolve for the comparison to the IP?

> 2. Configure dynamic DNS.

How does this help?  From reading the ml FAQ, I thought that dynamic
DNS still couldn't do anything about reverse resolution, or is this a
different issue?

4.18 Can I get my DYNDNS name to reverse resolve (like for IRC)?

The answer is no. The reason for this is based on the fundamentals of
the DNS as we know it today.

You can, given a name server, set an address record for any internet
site with relative ease. If you have a domain of
"mydomain.dyndns.ml.org", the DNS will check ML.ORG's nameservers for
the IP address corresponding to that name. However, if one does a
lookup on the IP address itself to get a name, DNS will check to see
which name servers are authoritative for that IP address, and will
likely find that it is your ISP's name servers. The DNS records for
what nameservers are authoritative for a given block of IP addresses
is maintained by the InterNIC (or its equivalent in other
locales). Even if we were to add a PTR record for you in our DNS, it
would not make a bit of difference.

Note that it IS possible, with help from your ISP, to sometimes get
reverse DNS to work. However, with regards to DYNDNS, don't even ask
because you get a different IP address each time. For those with FREED
names, this is much more plausible.

Rob Browning <rlb@cs.utexas.edu>
PGP fingerprint = E8 0E 0D 04 F5 21 A0 94  53 2B 97 F5 D6 4E 39 30

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