eMail Messaging Policy Framework

 

eMail Messaging Policy Framework (eMPF)

What it does
------------

   eMPF follows a set of administrator-defined rules describing
who can message whom.  With this, companies can segregate various
parts of their organizations email activities, as well as provide
a variety of security-enhancing services.

How it does it
--------------

   During an SMTP session, when a sender identifies themselves, either
via SMTP_AUTH, or via the message envelope, as well as a recipient,
eMPF loads applicable message policies to determine if the sender is
allowed to message the sender, and if the recipient is allowed to
receive mail from the sender.

What it doesn't do
------------------

   Because mail from outside your mail server cannot be authenticated,
the policy framework cannot be entirely sure about the identities of
senders messaging local users.  However, if SMTP_AUTH is enabled, and
required by your local users, it can prevent local users from transmitting
information to parties who should not view it.  It is HIGHLY recommended
that a mail server implementing eMPF also require SMTP_AUTH by it's local
users as well as use the POLICY_ENFORCE_AUTHENTICATION configuration so that
senders from the outside cannot masquerade as local users.

Policy configuration
--------------------

   A large, complicated policy may be rather intimidating at first, however,
if the rules are documented well, and a basic knowledge of the format of a
policy is known, they are rather simple to set up.

   comment:
   # text
   ; text
 
   policy:
   :,[,][,]

   user policy:
   :[]

   delivery policy:
   [(

[,

])]

   delivery types:
   L - Local
   R - Remote
   E - External
   I - Internal

Delivery types specify what types of messaging can take place.  An uppercase
delivery type allows a type of delivery, and a lowercase delivery type,
disallows a type of delivery.  Delivery types may take a list of addresses.
When a list of addresses is provided after a delivery type, those addresses
are the only addresses covered by that delivery type.

Certian delivery types apply only to either the sender of the recipient.
Here is a more clear definition of each of the delivery types.

   Local    - (Sender only) When sending a message to a user on the same domain
   Internal - (Recipient only) When recieving a messages from a user of the
              same domain
   Remote   - (Sender only) When sending a message to a user on another
              domain (even if that domain resides on the same mail server).
   External - (Recipient only) When receiving a message from a user on
              another domain (even if that domain resides on the same server).

Samples
-------

In this example, example.com allows all messaging.  In this case,
simply not defining a policy would be more efficient.

   example.com:LREI,

Now, example.com wishes all mail to stay internal.  As stated above,
there are particular cases in which eMPF cannot authenticate a sender.
This only occurs when a remote mail server is transmitting mail to a local
user on your system.  In this case, a remote user could pretend to be a local
user, and succesfully deliver mail to another local user.  However, the
recipient would be unable to message back.

   example.com:LIre,

As in the above example, example.com wants all mail to stay internal, however,
a few of their users are allowed to communicate with the outside world.  Sales
can communicate with everybody, and Tasks can send messages only to their
sister-site, example.org.

   example.com:LIre,sales:RE,tasks:R(),

Something to keep in mind in this scenario, is that if example.org is hosted
on the same system, and has similar policies to example.com, a policy must be
established for example.org which allows messages from example.com.

   example.org:LIre,sales:RE,tasks:E(),