Hi @Mike Furnival ,
What's the type of your account(POP or IMAP)? Did this issue occurred only recently or when you first configure your account in Outlook?
In order to further confirm if the issue is related to your Outlook, if it possible, it's recommended to log into your web mail to check if it could display the messages before 1 month ago normally there.
- If you could view all messages normally in your web mail, the issue may be related to your Outlook client. As I know, for IMAP account, we could set mail to keep offline like below, after that, it would display the messages within 1 month, please kindly check if it's also your case.
- If that's not your case and the issue occurred only recently, considering any view setting and filter may also cause it, if you don't have other custom view setting in your Outlook, please try to reset your view settings like below to check if the issue has any difference after that:
- If the issue still exists, in order to avoid any interference of corrupted Outlook data file, we could try to repair your data file for testing.
- If that's also invalid, due to it may also occur when the local Outlook profile is corrupted, it's recommended to recreate a new Outlook profile and readd your account to check if it could work for you(Control panel>Mail>show profiles>add>redd your account).
If your issue has any update, please feel free to post back.
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