Such issue generally occurs in outlook 365, when you attempt to download excel attachments from rights protected emails in outlook 365 inbox. Then error message pops up as “You are not signed into office with an account that has permission to open this workbook.”
How to fix this excel attachment issue in restricted emails.
- Draft a new mail in outlook 365.
- Select option Sensitivity.
- Open Help & Feedback.
- Navigate to Reset Settings then click on it.
- Restart outlook 365 and issue will be resolved.
You may also follow the above steps if any of the attachment fails to download from rights protected emails.
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