Hi @Ano Nymus ,
According to my research and search, I found an official document that describes how to manage trusted add ins in detail: Manage trusted add-ins for Outlook 2010, please refer to this article to see if it is different from your configuration.
Meanwhile, I found in the discussion of some posts that if you want to successfully start the security policy, you need to enforce outlook security settings. If you do not configure these related settings, it is suggested that you could refer to the settings of outlook security mode for configuration to check whether there are differences.
Considering that I don't know which method you use to get the hash value and the configuration of DLL, and we are unable to test the same three-party software, if possible, it is suggested that you could change the way to get the hash value and configure other trusted add in to check whether there is any difference.
Hope the above is helpful to you. Please contact us if you have any questions!
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