Hello Renée Kirby,
Thank you for posting this case in Microsoft Community!
Based on your description: How to revert to classic Outlook? I would like to cooperate with you working on this case. Since you do not have the option to toggle out of New Outlook in the top right of your screen, you may try following workaround to fix this case:
1. Firstly, you may try to check this Microsoft article Troubleshoot Outlook for Windows issues to re-install New Outlook for Windows.
Steps:
Once completed, you may check if the option to toggle out of New Outlook is showing in the top right of your screen.
2. If still not working, finally you may try to un-install your Office application from Control Panel completely and re-install the latest version of Office 365 application and check if working or not. Download and install or reinstall Microsoft 365 or Office 2021 on a PC or Mac - Microsoft Support
As for your another case, do you mean this mailmerge add-in refer to Use mail merge to send bulk email messages? If Yes, this feature is still not available yet in New Outlook. For my suggestion, you may apply other mailmerge add-in via going to New Email>Message>Apps>Add apps. Then you can search mailmerge add-in and check if useful to add to your New Outlook.
SecureMailMerge - free plugin on the store has supported for New Outlook: (Add-In store: SecureMailMerge )
I understand your concerns here but, please note Microsoft is constantly working on improving this product and adding more new features and the new Outlook for windows (Preview) version is still under active development. Therefore, I suggest keeping an eye on the Microsoft Outlook blog or the Microsoft 365 Roadmap | Microsoft 365 for any updates on this feature. In the meantime, I do apologize for the inconvenience this may cause, if you heavily rely on this feature, you may consider Toggling out of the new Outlook for Windows preview - Microsoft Support for now. I will also update here once I get additional information and the specific timeline for the feature will be added.
At this point, it is also recommended that click Help > Feedback or Contact support and provide feedback within the new Outlook for Windows and add your concern as an idea through the new Outlook in-app support Feedback site. Microsoft will keep monitoring customers feedback and valuable ideas there to consider/include in the future product update.
Your understanding and patience will be appreciated.
Thank you!
