What is the difference between SMTP Virtual Server and SMTP Connector in Exchange 2003?

What is the difference between SMTP Virtual Server and  SMTP Connector in Exchange 2003?

What is the basic role of each one?

Thank you.
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SMTP virtual  server:
An SMTP virtual server is an SMTP protocol stack (a process or server that both receives e-mail messages and acts as a client for sending e-mail messages). Each SMTP virtual server represents an instance of the SMTP service on a server. An SMTP virtual server is defined by a unique combination of an IP address and port number. The default SMTP virtual server uses all available IP addresses on the server and uses port 25 for inbound connections. A single physical server can host many virtual servers.  You use Exchange System Manager to control most of the SMTP settings.  It uses its own SMTP connector to send email to the Internet.

SMTP Connector:
SMTP relies on DNS to determine the IP address of its next destination server. To send mail directly to an external mail server, an SMTP connector must use DNS to resolve external domain names. Alternatively, the connector can simply forward mail to a smart host that assumes responsibility for DNS name resolution and delivery.

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SAM2009Author Commented:
Thank you guys for your comments, but could you give an exemple when mutiple SMTP Vitual Servers are used?
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Exchange 2000 and 2003 allows creating multiple SMTP Virtual servers on a single Exchange computer.  Obviously those SMTP Virtual servers need to be logically separated. One SMTP Virtual server is designated as Inbound SMTP Virtual Server and is handling e-mail traffic from the Internet and another SMTP Virtual Server is handling outbound traffic. The easiest way to create multiple SMTP Virtual Servers is to assign them to different IP addresses.  In the case of a dual homed computer those IP addresses are assigned to different NICs.  In the case of a server with a single NIC multiple IP addresses can be assigned to that single NIC.

Hosting the SMTP connector for the Internet on the appropriate SMTP virtual server, ensures that only that virtual server passes outbound mail going to the Internet.  Pointing MX records or smarthosting SMTP servers in the DMZ to the IP address of the second SMTP Virtual Server ensures that all e-mail traffic going through it is inbound to the organization.

Having such design in place you can apply different filtering and other security policies to SMTP Virtual Servers separately.  For example if you want to implement sender filtering of specific internal aliases (to mitigate the problem of them being spoofed from the Internet) you can enable such filtering on the Inbound SMTP Virtual Server only.  Thus, outbound e-mail flow will not be affected by such filtering.

If you have a spam filtering solution that runs on Exchange 2003 gateway platform (such as IMF or Brightmail) you can bind that solution to the Inbound SMTP Virtual server.  This way your outbound mail won’t be scanned for spam which could result in performance wins.

With the two SMTP virtual server approach you can control inbound vs. outbound e-mail traffic through this gateway separately.

As an added benefit of the above design, you get more convenient monitoring of inbound and outbound Internet mail flow going through this gateway.  Performance Monitor has separate instances of SMTP counters for each SMTP Virtual Server.
SAM2009Author Commented:
Thank you for all your informations and links.
You're welcome.  Glad to do it and thanks for the points!
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