That registry value by itself does absolutely nothing. Its purpose is to tell Outlook to look in a particular Exchange public folder to get information about what security settings it should implement. There is no security setting that would allow a single external program to send messages without prompts. It's an all-or-nothing issue. If you let that third-party app send, you let all external apps send, including those that propagate viruses.
See http://www.outlookcode.com/d/sec.htm for your options with regard to the "object model guard" security in Outlook 2000 SP2 and later versions.

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Sue Mosher, Outlook MVP
Author of Configuring Microsoft Outlook 2003
http://www.turtleflock.com/olconfig/index.htm
and Microsoft Outlook Programming - Jumpstart for
Administrators, Power Users, and Developers
http://www.outlookcode.com/jumpstart.aspx
> Steve,
> There is an Outlook 2003 registry key that you can add.
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>> I know there's an option to suppress this dialog box in Outlook Express 6,
>> but I couldn't find it in Outlook 2000 SP3.