[ale] reverse DNS & spam (was: godaddy for DNS)

[John Heim]

Wait a minute, something doesn't make sense to me. Why would a mail system 
do a reverse lookup as a way to prevent spam? So the smtp client connects to 
the mail server, the socket says the connection is from 66.170.20.226 and 
the smtp headers say its from lists.iavit.org. If you lookup 
lists.iavit.org, it does resolve to 66.170.20.226. That should be fine 
because if I'm a spammer and I'm using an account  on 66.170.20.226, I'm 
going to say I'm  somebody *else*. You know, I say I'm 
Bill.Gates at microsoft.com or something.   If you lookup microsoft.com, you 
don't get 66.170.20.226. Really, just the fact that lists.iavit.org and 
iavit.org resolve to the IP address of the smtp client should be enough. How 
is a spammer going to fake that? Yeah, I'm sure they could but it would be a 
heckuva lot of work.

There is this SPF record thing where it asks the DNS server for hosts 
allowed to send mail for that domain. That makes sense to me. I can 
understand that. But I don't get the reverse lookup thing. It seems to me 
that would block a lot of legitimate mail for no reason.

Maybe I'm getting "reverse DNS" mixed up with something else.A forward 
lookup is when you take a name and get an IP address from it. Reverse lookup 
is when you take the IP and get its name. Right?

From: Crawford Rainwater
Sent: Thursday, December 29, 2011 11:22 AM
To: ale at ale.org
Subject: Re: [ale] godaddy for DNS

John and company:

You have two options actually.
(1) Use GoDaddy for all of your DNS records.  However, reference another 
posting about the GoDaddy exodus due to their changing SOPA position.
(2) Use your virtual machine as one DNS server and a second for a DNS slave 
server.  My personal choice since some ISPs and hosting groups can cause 
issues with rDNS (reverse DNS) matching of email (part of spam 
detection/prevention in some cases) and such.  You would have your domain 
name registrar associate/register the domain's DNS with both of these (e.g., 
ns1.example.com and ns2.example.com for example.com) which comes up on a 
"whois example.com" typically at the bottom of the record.

HTH.

--- Crawford

The Linux ETC Company
10121 Yates Court
Westminster, CO 80031 USA
voice:  +1.303.604.2550
web:    http://www.linux-etc.com

Please do not print this email unless it is absolutely necessary.  Be 
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----- "John Heim" <john at johnheim.net> wrote: -----
>
> Hi, I have a donated virtual machine to use for a non-profit. Its for
> the
> International Association of Visually Impaired Technologists (IAVIT).
> I've
> registered iavit.org at godaddy. But I'm a little confused as to what
> DNS
> records I need in order to get mail (postfix, dovecot) and lists
> (mailman)
> to work. I need email addresses like john at iavit.org to work and
> addresses
> like announce at lists.iavit.org to work.
> What I have at the moment is an A record with a blank host name
> pointing to
> the IP of our VM, another A record for lists that points to the same
> IP
> address. I wasn't sure you could have 2 A records pointing to the same
> IP
> address but it seems to work. Then I have CNAME records for www and
> wiki
> pointing to lists.
>
> Can I point godday to a DNS server on the virtual machine itself? I
> tried to
> do that but it balked. For one thing, it said I needed 2 DNS servers.
> I'm
> not sure what the point of that is because iif DNS is down on the VM,
> nothing else on the VM is going to work anyway.
>

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