Hi @Georges Carraha ,
1.Do you have mailboxe enabled for this security group? If not, enable it with the following PowerShell command.
In addition, the scope of the security group cannot be set to Global (it will fail to enable), it is recommended that you change it to Universal.
Enable-DistributionGroup -Identity "securitytest"
2.You can try to recreate the Outlook profile or create a new OAB and assign it to the database, please refer to the steps in this post: Outlook send/receive download address book error.
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