The Cloudmark add-in is recreating its toolbar each time you start OUtlook. THerefore, if you want to hide it, you'll need to hide it each time you start Outlook. If you want Cloudmark to provide an option to show/hide the toolbar, you might want to make that suggestion directly to them.

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Sue Mosher, Outlook MVP
Author of Microsoft Outlook 2007 Programming:
Jumpstart for Power Users and Administrators
http://www.outlookcode.com/article.aspx?id=54
>I installed Cloudmark Spam filter software and it loads
> in the Toolbar.
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>
> There is no setting in Cloudmark for this.