Outlook 2010 Beta has a bug in the 'prompt before deleting' checkbox – deselecting the checkbox at Options, Advanced, Prompt for confirmation before deleting doesn't actually work and you’ll still be prompted. It's fixed in later builds but until then, users can edit the registry to disable the prompt.
At Start menu, Search field or Run command, type regedit and browse to the following key and create the WarnDelete value.
Value: 1 (checked) or 0 (unchecked)
Published March 26, 2010. Last updated on June 1, 2014.