How to block outgoing messages to all external domains and allow outgoing messages to selected external domains in Exchange 2003

There is no straight forward method to block all outgoing messages to external domains in Exchange 2003, but you can do it using simple method depicted below.

Steps are given below so that you can easily archive this.

Step –1 

Create Deny SMTP connecter in Exchange 2003 - Block outgoing to all external domains.
Open Exchange System Manager >> Expand Administrative Groups >> Routing Groups >> First Routing Group >> Right Click Connectors > New >> SMTP Connector

Name: Connector Name
Forward all mail through this connector to the following smart hosts: Type a Bogus Name (should not exist in the network)
Local Bridgeheads: Select the Local Server

In Address Space >> add a address space "*"  >> Apply >> OK

Step - 2
Create Allow SMTP connecter in Exchange 2003 - Allow Outgoing to selected external domains
Open Exchange System Manager >> Expand Administrative Groups >> Routing Groups >> First Routing Group >> Right Click

Connectors >> New >> SMTP Connector

Name: Connector Name
Forward all mail through this connector to the following smart hosts: Email Relay Server or Use DNS route to each address space on this connector option
Local Bridgeheads: Select the Local Server
In Address Space >> In the Address Space >> add all domains that you need outgoing mails delivered >> Apply >> OK

Step - 3
Disable the non-delivery reports \ delay delivery reports – This is required cause all messages are sent to deny parties will be queued in the server to flush them quickly you can modify the settings as appropriate.
Open Exchange System Manager >> Expand Global Settings >> Internet Message Formats >> Double click the Default Policy >> Advanced >> un-tick

Step - 4
Send a Test Mail from Outlook or OWA

Step - 5
Open the Queue
Open Exchange System Manager >> Administrative Groups >> First Administrative Group >> Server >> server.name >> Queues

Make sure all outgoing messages are stuck in the queue except allowed domains

Step - 6
Modify the default delivery \ delay notification values in the SMTP Virtual server

Open Exchange System Manager >> Administrative Groups >> First Administrative Group >> Servers >> server.name >> expand the Protocols >> SMTP >> Double click Default SMTP Virtual Server >> In the Delivery tab >> Change them

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-Thanks
@ Roshan