Hi Alexandro,
Please try the following steps and see if it works:
1. Go to File > Account Settings > Account Settings > Tab Address Book. If the Outlook Address Book service has not been added to the Mail Profile, please select "Additional Addreee Books", Next, choose Outlook Address Books, Next, restart
Outlook and check the result.

2. If the Outlook Address Book Service has been added already or the above doesn't work, please right click the Contacts folder, choose Properties > Outlook Address Book, select the checkbox of Show this folder as an e-mail Address Book:

3. If the above doesn't apply or the issue persists, the issue may be caused by the corrupted Outlook Address Book service. Please try recreating the Outlook profile and check if it can be fixed:
Create an Outlook profile
Hope this can be helpful.
Regards,
Yuki Sun
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