Using New Outlook on Windows for personal email, calendar, and contact management
Hello Hugh Aldous, Thank you for posting this in our community.
I completely understand how important the Thesaurus is for improving the quality of your emails. At this time, the New Outlook does not include the Review tab or Thesaurus. However, you can switch back to Classic Outlook to continue using these features. Another option is to draft your emails in Microsoft Word, which offers the full Review tools, and then copy them into Outlook.
I believe Microsoft are actively working on adding more editing capabilities in future updates. You can also submit feedback directly through Outlook by selecting Help > Feedback to help prioritize this feature.
Kind regards,
John Oli