Using Classic Outlook on Windows for personal email, calendar, and contact management
Hi JulieMaycock,
Thank you for your update.
Based on your mentioned description, we understand that you have Office 365 Exchange mailbox account and you can see missing emails under Outlook Web app client side, if so, at once we would like to suggest you please open Outlook application in safe mode in desktop client and see if you can see the emails or not. For safe mode > press Windows 10 + R keys > type outlook.exe /safe.
If the issue persist, kindly try to resolve the issue by using SaRA tool. This tool will further help you to identify the issue for Outlook or system. So, kindly try to download Sara Tool and sign in with your work or school account and select the Outlook related issue.
Here is the download link: SaRA tool
For more information about the tool, see Automatically diagnose and fix Outlook issues.
Meanwhile, if the missing emails are available under Outlook web app, could you please provide us the detailed screenshot about at which place the missing emails are available on Outlook web app?
To uploading screenshot > click on Image symbol > browse the captured screenshot image from the computer, click on Upload button.
Regards,
Darpan