Microsoft is investigating a known issue that prevents some Classic Outlook users from sending emails via Outlook.com, causing non-delivery reports and a permissions error (0x80070005-0x0004dc-0x000524). Microsoft recommends temporary mitigations—removing the M365 Address Book, hiding the Outlook.com contact from the tenant GAL, creating a new Classic Outlook profile, or using New Outlook/Outlook on the web—while it continues to investigate. #ClassicOutlook #ExchangeOnline
Keypoints
- Affected Classic Outlook users receive NDRs indicating messages could not be sent and a permissions error code 0x80070005-0x0004dc-0x000524.
- Failures are more frequent when the Outlook.com account is in an Outlook profile linked to another Exchange account or when an Exchange Online mail contact shares the same SMTP address.
- Microsoft advises removing the M365 Address Book or hiding the Outlook.com contact from the Microsoft 365 Global Address List (GAL) to reduce address lookup conflicts.
- Workarounds include creating a new Classic Outlook profile containing only the affected account or using New Outlook or Outlook.com on the web to send email.
- Microsoft recently fixed other Classic Outlook issues and is also investigating EWS-related group-creation connection errors and a mouse-pointer disappearance bug.