Hi @Gladys Tang @ Work ,
What's the version of your Outlook 2016(File>Office account>About Outlook)? Based on my research, the @mention feature is introduced after Office 365 ProPlus version 1609 (Build 7369.2024) and Office 2016 Version 1609 (Build 7369.2118), so please first check your version of your Outlook client with them.
Then, the @mention feature also has the requirement of account, as the official article mentioned, "The Mentioned mail feature and the @ (at symbol) indicator are only available for recipients using Exchange Server 2016, Exchange Server 2019, Exchange Online, or Outlook. com." please check if your account could support this feature.
If you have checked them but the issue still exists, in oder to further confirm your issue, please provide me with more information about it:
- Has this issue occurred only recently? If so, have you performed any specific operations before it?
- Could you use this feature in your web mail?
If your issue has any update, please feel free to post back.
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