Hi @NepaleeSandhya ,
Thank you for posting your question in the Microsoft Q&A forum.
Here is the information you need.
- You can choose either Unified manifest for Microsoft 365 or Add-in only manifest. They both support Outlook add-ins.
- Spam reporting supports both on Classic Outlook and New Outlook.
You can find more details at:
Office Add-ins manifest - Office Add-ins | Microsoft Learn
Feature comparison between new Outlook and classic Outlook - Microsoft Support
I hope this information helps.
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