CHAPTER 15
SMTP TRANSPORT
CONFIGURATION
As its name implies, it is a simple protocol. The core transport engine of Exchange
20000 Server is SMTP service of Microsoft Windows 2000. SMTP is very
efficient transport protocol; it can transfer messages, for instance, up to 300% faster
than X.400.
Lesson 1:
SMTP Configuration and Virtual Servers
By default, every Exchange 2000 server relies on one SMTP virtual server for its
communication with other servers in the local routing group. Use and remote SMTP hosts
don’t to authenticate themselves before they can communicate. Anonymous access to the
local SMTP service is generally allowed. Nevertheless, you can restrict access through
authentication and encrypt the
communication.
Configuring Additional SMTP Virtual Servers
One SMTP virtual server is usually sufficient for Exchange 2000 Server, but there are
situations in which multiple virtual servers can be helpful. Each virtual server must be a
unique TCP socket, (that is, IP address
+ TCP port).
NOTE: Adding additional virtual servers does not increase the server’s scalability or
performance. Each SMTP virtual server operates with multiple threads being able to handle
tasks concurrently.
Working with Additional Virtual Servers
You can control virtual servers and start, stop, or pause them independently of each other.
Pausing a server prevents the establishment of new connections, and existing connections are
not terminated.
NOTE: Stopping virtual servers in Exchange System Manager leaves the SMTP service running
on the computer. Stopping the SMTP service itself, on the other hand stops all virtual servers.
When you restart the SMTP service, only those virtual servers that originally were active when
the service was shut down will be
activated.
=======================================================================
winexc15.html
PAGE 2
2002/06/26
Mailroot Directories of Virtual Servers
Every SMTP virtual server has a separate Mailroot directory. All Mailroot directories are
located under \Program Files\Exchsrvr\Mailroot and are named sequentially, for example, Vsi1,
Vsi2, and so on.
NOTE: The Exchange 2000 Setup program moves the Mailroot directory of the SMTP service
from \Inetpub\Mailroot to Program Files\Exchsrvr\Mailroot. The old folder structure will not
be deleted, but any messages in the former Pickup and Queue directories are not delivered.
To send them, move them to the Pickup directory under the new location. (VS = Virtual server,
and Bad Mail – NDR or non-delivery
report.
Managing Incoming Message Traffic
Let’s assume the Exchange 2000 server is supposed to accept messages from any host on the
Internet. How does a remote Internet host find the SMTP virtual server to transfer messages
to it? You will need to make sure that the Internet hosts are able to resolve your domain name
to your host’s public IP address. Typically, DNS provides the required name resolution
functionality, as explained in
Chapter 11, “Internet-Based Client Access”.
IMPORTANT For other SMTP servers to find your SMTP server on the network, your
SMTP domain name must be registered in the Internet DNS
(mail exchanger, or MX records.)
Controlling Incoming Connections
As soon as your host is connected to the Internet and publicly registered in DNS, all Internet
hosts are able to find it, connect to it and transfer messages. Every connection consumes
server resources, so numerous simultaneous connections can decrease system performance.
By default, Exchange 2000 Server does not enforce any limits. The default timeout is 10 minutes.
You can also specify a limit for the number of inbound
connections.
Inbound E-Mail Domains
The recipients container, select Recipient Policies, than then in the details pan, right-click the
desired policy, such as Default
Policy.
=======================================================================
winexc15.html PAGE 3
2002/06/26
Controlling Message Relay
By default, Exchange 2000 Server allows only authenticated computers to relay SMTP messages.
An advertiser might configure his or her Internet mail client to send messages to your SMTP host
if it accepts message relaying for anybody. Now, all the advertiser has to do is compose one new
message, specify thousands of recipients conveniently from a database, and then send this one
message to the relaying host.
Configuring Message Filters
Delivering unnecessary Internet messages is a drain on your system resources; it decreases the
productivity of the knowledge worker; and there is always a risk of receiving viruses contained
in message attachments.
You should use wildcards (*) where possible. To filter for entire Internet domains, for instance,
use a wildcard as follows: *@makeabillioneveryday-times-100.com.
By default, Exchange 2000 Server accepts messages for delivery to up to 5,000 recipients.
Messages with more recipients are returned undeliverable. However, the settings specified at
this location apply only to users with mailboxes in the organization. Limits can be overwritten
per user in Active Directory Users
and Computers in the user account’s Exchange general tab.
If you allow anonymous users and SMTP hosts to relay through your Exchange 2000 Server,
up to 64,000 recipients are accepted per message, because the settings of the SMTP virtual
server apply instead of global
delivery settings.
Forwarding Messages with Unresolved Recipients
If you examine the Messages tab further, you will discover the Forward All Mail With Unresolved
Recipients To Host text box, which allows you to specify the fully qualified domain name (FQDN)
of another host for delivery of
messages that contain unresolved recipients.
NOTE: To avoid message loops, do not forward messages for unresolved recipients to another
virtual server if this server is
also configured for forwarding of unresolved messages.
NOTE: The forwarding of nondeliverable message to another SMTP host affects messages form
Internet and MAPI-based clients. If you use this feature to support non-migrated users, keep in
mind that nondeliverable messages of MAPI-based clients, such as Outlook 2000, will only contain
a WINMAIL.DAT attachment and may not be readable by non-MAPI clients. It is not advisable to
use the forwarding of nondeliverable messages for long-term coexistence.
=======================================================================
winexc15.html PAGE 4
2002/06/26
Managing Outgoing Message Traffic
The configuration of outgoing message transfer primarily concerns the notification of local users about
the delivery process. By default, an SMTP virtual server attempts to deliver a message as soon as it
arrives. If the remote host is unavailable at that time or if a communication failure occurs, the virtual
server queues the messages for
delivery at later time.
Optimizing Outbound Connections
Per domain, 100 concurrent connections are allowed by default. If you have a large number of
messages to transfer between SMTP hosts, you might increase the number of connections, but the
remote host must be able to accept them. In a default configuration, Exchange 2000 Server is able
to open up to 1000 concurrent connections to multiple Internet domains and deliver messages to
them at the same time. (ANONYMOUS).
TCP is always used for SMTP.
Smart Host Message Transfer
In most cases, you should not change this setting because it affects all connections. Internet hosts,
for instance, generally expect
incoming connections on port 25.
Smart Hosts rely through a proxy or a firewall.
Direct Message Transfer
If you don’t use a smart host for message delivery, your SMTP virtual server must be able to resolve
e-mail domain names into
corresponding IP addresses itself.
NOTE: By default, Exchange 2000 Server uses DNS to
locate remote SMTP hosts.
=======================================================================
winexc15.html PAGE 5
2002/06/26
Automatic Replies to the Internet
Automatic message relies are system messages, such as delivery and nondelivery reports,
out-of-office responses, read and nonread receipts, and messages automatically forwarded by
means of Inbox rules. By default,
these message types can be sent to Internet recipients.
Communicating with Other Exchange Organizations over the
Internet
Your users will communicate with many Internet domains that actually correspond to other
Exchange organizations. After all, Exchange 2000 Server is one of the world’s most popular
messaging systems. In Exchange organization, users typically work with MAPI-based clients,
such as Outlook 2000, that support advanced rich text information in e-mail messages. The
Default message format definition object allows the user to decide whether to send Exchange
rich text information in Internet
messages.
Configuring Protocol Logging
You can also use protocol log information to verify whether the virtual server is performing its
work as expected or it experiencing communication problems. Last but not least, SMTP
protocol logging can help to
identify attacks from the Internet.
Exercise Summary:
sender the ability to transfer messages.
Lesson 2:
Customizing the SMTP Service
Most important, SMTP extensions give you a means by which you can examine messages
for critical or unsafe content and
block their transmission or delivery.
SMTP Transport Event Handling
Event sinks rely on Microsoft Collaboration Data Objects 2.0
(CDO 2.0).
=======================================================================
winexc15.html PAGE 6
2002/06/26
Exchange 2000 registers numerous SMTP and NNTP event sinks to integrate the existing
Windows 2000 services with the Information Store.
Protocol Event Handling
SMTP protocol events allow you to alter the way the SMTP service communicates with
other SMTP-based systems. Exchange 2000 Server, for instance, implements a variety of
SMTP protocol event sinks, which propagate, among other things,
link state information across the
communication infrastructure.
There are two types of protocol events that the SMTP service
allows you to intercept:
local SMTP service and establishes a session by sending the HELO
or EHLO command.
SMTP host and
establishes a session to transfer messages.
Event Binding
For the SMTP service to work with your event sinks, you need to register them in the IIS
metabase. A binding associates a particular event, such as OnArrival, with a sink name,
such as SMTPMessageCheck. Within the metabase a globally unique identifier (GUID)
identifies each binding.
Virus Protection Using Transport Event Sinks
A virus scanner, for instance, can use them to check all incoming messages and safely discard
those
that contain infected file attachments.
Mail worms follow a very simple principle. A recipient opens an infected message attachment,
and the virus code is executed. This retrieves the full set of address information from all available
address lists to or from messages in the inbox, and a new message addressed to all recipients is
generated.
Exercise Summary:
such as an official note that this message was received from an insecure network; or perform a
basic virus scan.
=======================================================================
winexc15.html PAGE 7
2002/06/26
Chapter Summary:
many subdirectories exists, depending on the number of SMTP virtual servers that have been
configured.
Typically, one virtual server can handle all SMTP-based message
transfer.
that incoming messages are delivered to your server. Your SMTP domain name must be
registered in an
MX record in the Internet DNS.