Re: DNSs, MXs and RBLs....

[Santiago Barahona <sant-bar () dsv su se>]

Hi all,

First of all, many thanks for taking some of your time to help me...
Second, we are not in the business of spamming people... or at least I  
hope we're not...  =)
Third, I know if the mail servers of the company I work for have been  
or not blacklisted, I'm new...

Let me put this as clear and simple as possible:

1. There are two DNSs controlled by different entities and one mail  
server: DNS-A, DNS-B and Mail-B (being DNS-A owned by co.A and DNS-B  
and Mail-B owned by co.B.)
2. The mail server will start sending and receiving mails on behalf of  
co.A
3. To do this, the IT guys in co.B say the records in DNS-A from [co- 
a.com IN MX mail.co-a.com] to [co-a.com IN MX mail.co-b.com]
....
so when someone tries to reach co-a.com to send an email it will be  
redirected to the mail servers in co.B...

I was wondering, if an anti-spam solution (RBLd, DNBL....) before  
blacklisting an IP it may do some tests to verify it is spamming IP...  
would this type of configuration be perceived as such?

Thanks again,

Santiago



On 21 Mar 2008, at 14:35, Ned Fleming wrote:

> On Thu, 20 Mar 2008 19:26:19 +0100 (CET), "Santiago Barahona"
> <sant-bar () dsv su se> wrote:
>
> > Once upon a time, there were two companies that created one new  
> > entity
> > (let's say 50-50)... one of them provides the IT infrastructure and  
> > the
> > other "the name" (i guess): it is company A's mail servers, and  
> > company
> > B's domain name...
> >
> > Since the new users will be in company A's infrastructure, their  
> > mailboxes
> > will be hosted in company A's mail servers... but the domain name  
> > will be
> > controlled and hosted by company B... to do this someone has  
> > suggested to
> > company B to modify their DNS entries to point to company A's domain
> > name....
>
> OK, you have three zone files: oldcoA.com, oldcoB.com, and newco.com.
>
> > So when a MTA tries to reach user () newco com, it will find in  
> > Company B's
> > DNS that it points out to companyA.com, then it will go ask a DNS  
> > who is
> > companyA.com and deliver the mail... (tell me if I'm wrong)...
>
> Whoever controls the DNS zone file for newco.com will control the IP
> address for the MX record(s) for that domain. That IP address might be
> at oldcoA or oldcoB or somewhere else.
>
> Now, if user () newco com is an alias for rumpelstiltskin () oldcoA com, and
> the email needs to go there, then you will need a map of some type
> (depending upon your MTA, i.e., postfix, sendmail, etc.) that
> redirects the email to its proper destination. Easy to do.
>
> > At first glance it looked OK but then it started to cause me  
> > trouble when
> > I thought about the case when the users of this domain start  
> > sending mails
> > because I think that company A's mail servers risk of being "black  
> > listed"
> > by some RBLs... if this happens not only the users of the new  
> > entity will
> > be percieved by spam but all users that use those servers...
> >
> > Any light??... is it possible to get blacklisted this way??... do  
> > you have
> > any suggestions on how to avoid the risk??
>
> I don't see how you can be blacklisted, unless one or the other of the
> oldcos IP addresses was blacklisted to begin with, in which case it
> could extend to email from newco.com
>
> > or should make a risk analysis and present it to management in  
> > order to
> > get it to be accepted or not??
>
> If either of the oldcos is blacklisted, then this is a good idea.
>
> Ned