Microsoft fixes Classic Outlook bug causing email delivery issues
ID: 593739ab-55b3-5efc-8cc9-af3ae8225dab
STIX ID: report--593739ab-55b3-5efc-8cc9-af3ae8225dab
Feed Name: Bleeping Computer
Microsoft implemented a server-side fix on April 3, 2026 to resolve a Classic Outlook issue that caused some users to receive non-delivery reports (error 0x80070005-0x0004dc-0x000524) when sending or replying via Outlook.com; affected users are advised to use the New Outlook or Outlook.com on the web or apply provided workarounds. The notice also references additional Classic Outlook and Exchange Online issues under investigation but contains no indication of malicious activity.
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