Hi @Eli Spetgang ,
Welcome to Q&A!
As I know, the situation you mentioned above is quite normal and is by designed.
In Outlook, in order to ease management and avoid confusion, Office add-ins are all synced along with your email account. And you could manage your Office add-ins via the Office Store, for more information, please check: Get an Office Add-in for Outlook.
So, if you would like to use the same add-in in other mailbox, you need to add this specific add-in to your other email accounts. For example, you could add it via the Get-Addins options like below:
Hope this can be helpful.
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