Microsoft links Classic Outlook issue to email delivery problems

Microsoft is investigating a known issue that prevents some Classic Outlook users from sending emails via Outlook.com, producing non-delivery reports and permission errors (e.g., 0x80070005-0x0004dc-0x000524). The bulletin explains conditions that may trigger the error (such as an Exchange Online mail contact sharing the same SMTP address or a linked Exchange profile), lists temporary workarounds (hide the contact in GAL, remove the M365 address book, create a new classic profile that only includes the affected account, or use New Outlook/Outlook on the web), and notes other recent fixes and ongoing bug investigations.