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Dear Clair,
Some reasons may cause the issue
- The Outlook issue.
Check whether the emails is in the spam or junk folder. If yes, it may be a email setting issue. I suggest you post in the Outlook category on our forum for further help.
- The account issue
If it is convenient, I suggest you use another account to do a test to see the result.
- The SharePoint feature issue
It may be that there are some email delay or email trigger issue in SharePoint Online in your tenant. It seems that you are the external user to the shared file's owner tenant. If yes, I suggest you let the tenant administrator there invites you as a guest to their Microsoft Entra and then I'd like you to access the shared file via the link to see whether you can access the file there.
Quickstart: Add a guest user and send an invitation - Microsoft Entra External ID | Microsoft Learn
- A temporary issue
If the issue has persisted for a long time, I suggest you let the tenant administrator there follow the steps in Get support - Microsoft 365 admin | Microsoft Learn to open a support ticket to our related team as soon as possible.
About admin roles in the Microsoft 365 admin center - Microsoft 365 admin | Microsoft Learn
How do I find my Microsoft 365 admin? - Microsoft Support
The administrator should be able to open the support ticket from Help & support in the Microsoft 365 admin center.
Then you can select the Phone support or the Email support as follows.
Thanks for your effort and hope that the issue can be soon fixed by our related team.
Sincerely
Cliff | Microsoft Community Moderator