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RE: Restricting Incoming Email in Exchange by From Address
From: "Dan Denton" <ddenton () PAYLESSOFFICE com>
Date: Tue, 21 Jun 2005 10:31:07 -0500

No additional security checking is involved here, but why not use the
Exchange General/Delivery Restrictions screen (Under user properties in
AD) to limit who the user can receive email from? Domain or Proxy server
authentication to an OWA server should take care of the authentication
issue.  

-----Original Message-----
From: Greg Jones [mailto:grjones () gmail com] 
Sent: Monday, June 20, 2005 6:03 PM
To: Steve
Cc: security-basics () securityfocus com
Subject: Re: Restricting Incoming Email in Exchange by From Address


Without explaining why, some of our employees require pop/imap access to
our exchange server from the Internet (they only need this for
receiving mail, and don't need smtp).   So when email from the
Internet comes in from a @mydomain.com address, I want to make sure that
whomever sent it is authenticated (using exchange), and reject the
traditional unauthenticated SMTP traffic when the From address is a
@mydomain.com address.  I will look at SPF more, but it seems to me that
what I'm trying to do should be pretty simple and effective.

Thanks

Greg

On 6/20/05, Steve <securityfocus () delahunty com> wrote:
Not sure I follow on the first part.  Your users can connect to your 
Exchange server via other clients like POP? If so, turn off POP/IMAP.

For spoofing/phishing check out using reverse DNS lookups with 
Exchange and/or SPF.  That will improve your overall email security.

STEVE
----- Original Message -----
From: "Greg Jones" <grjones () gmail com>
To: <security-basics () securityfocus com>
Sent: Saturday, June 18, 2005 12:30 PM
Subject: Restricting Incoming Email in Exchange by From Address


In Exchange (any version), I would like to disallow email coming from 
the Internet (smtp) that has a From address of my domain.  This would 
force our employees to use OWA or Exchange (via VPN of course).  This 
would help with phishing and worms that are fooling some of our 
employees (e.g., emails from admin () mydomain com).  Is this possible?

 Greg







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