RE: Protecting an Exchange server?

[Chris Santerre <csanterre () MerchantsOverseas com>]

Jose's recomendation below are quite good. We use Sendmail box in a dmz. Of
course I use Spamassassin. (See link in sig!) Email has to go thru firewall
twice before entering internal exchange server. IMHO no microsoft box should
ever be attached directly to the internet. 

You can setup aliases to users, then a static route to internal server. This
way you don't have to have actual users on the outside box, and the outside
box will handle rejections. There are a few other neat things you can do as
well ;)

Jose, I'm interested in your secure OWA setup. Is there more info you can
send me off list? Currently users outside the company have to VPN in to
check email. I'd rather just shut that off :) 

Chris Santerre 
System Admin and SARE Ninja
http://www.rulesemporium.com
'It is not the strongest of the species that survives,
not the most intelligent, but the one most responsive to change.'
Charles Darwin 

> -----Original Message-----
> From: Jose Enrique Diaz Jolly [mailto:enrique.diaz () cbbanorte com mx]
> Sent: Saturday, May 15, 2004 1:51 PM
> To: Mark G. Spencer; security-basics () securityfocus com
> Subject: RE: Protecting an Exchange server?
> Importance: High
>
>
>
> Sure there are several methods, some of them are expensive on 
> cash other
> on time and fine tuning.
>
> We have a strong policy against exposing any one whose surname is
> Microsoft to the internet. So we have made different schemas for
> different services. 
>
> For SMTP we have an SMTP server, sendmail on a linux box with some
> filters on it like Spamassassin, bogofilter etc. This server 
> verifies if
> the destination address is a real recipient using some of the sendmails
> LDAPRouting features against the inside network's Active Directory. We
> only have a single cluster with Exchange so I don't need the ability to
> route mail towards different servers to reach the recipient's mailbox.
> Thus facilitates me to ensure that any generated "rejection" is made by
> my linux box which is on my DMZ. No Exchange is "announced". Then
> instead LDAPRouting, I pass (deliver) all mail to an inside 
> server which
> has all the TrendMicro Security Suite, AntiSPAM and AntiVirus software
> which finally delivers to the actual Exchange. On the other hand
> outgoing mail is delivered to another box (smart relay) which also has
> sendmail on linux.
>
> The other feature is serving OWA, we revised MS' recommendation about
> serving securely OWA with an ISA server but I was not satisfied, so we
> started to work on a reverse proxy (a reverse proxy is a proxy by
> another name) built with Apache, again on a linux box. Using some
> features such as rewrite and proxypass I can serve owa without
> announcing nor letting it to be seen my OWA server.
>
>
> > -----Original Message-----
> > From: Mark G. Spencer [mailto:mspencer () evidentdata com] 
> > Sent: Thursday, May 13, 2004 12:52 PM
> > To: security-basics () securityfocus com
> > Subject: Protecting an Exchange server?
> >
> > Hello,
> >
> > I'm wondering if there is any way to locate an Exchange 
> > server on my internal network and place some kind of email 
> > appliance on our DMZ to actually send and receive email to 
> > the world and to the Exchange server on my internal network?
> >
> > Basically, I don't want my Exchange server to be accessible 
> > to the world in any way.
> >
> > So ..
> >
> > Internet -> My Email Appliance -> Firewall -> Exchange Server
> >
> > I envision setting up a dedicated route in the firewall 
> > between the email appliance out on the Internet and my 
> > Exchange server behind the firewall on my local network?
> >
> > Are there any email appliances that can work with Exchange in 
> > this way?
> > It's my (limited) understanding that Exchange server can't 
> > "pop" to another email server to pull each Exchange users 
> > email, so I'm not sure exactly how or if my plan could be put 
> > into action.
> >
> > Thanks,
> >
> > Mark
> >
> >
> >
> >
> >
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---------------------------------------------------------------------------
Ethical Hacking at the InfoSec Institute. Mention this ad and get $545 off 
any course! All of our class sizes are guaranteed to be 10 students or less 
to facilitate one-on-one interaction with one of our expert instructors. 
Attend a course taught by an expert instructor with years of in-the-field 
pen testing experience in our state of the art hacking lab. Master the skills 
of an Ethical Hacker to better assess the security of your organization. 
Visit us at: 
http://www.infosecinstitute.com/courses/ethical_hacking_training.html
----------------------------------------------------------------------------