Hi,
I understand that you want to use the Outlook Instant Messaging feature.
You're able to enable this feature via File > Options > Contacts in the versions earlier than Microsoft Outlook 2010.
Now in Office 365, please follow the steps below to enable this feature.
- Go to File > Options > People.
- On the "Online Status and Photographs" tab, check the box of the options "Display online status next to name".

Then you will be able to use the Outlook Instant Messaging feature.
Hope this can be helpful.
Regards,
Aidan Wang
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