Microsoft recently announced that it has resolved an issue that had been disrupting email delivery for users of Classic Outlook. Previously, some users attempting to send emails via Outlook.com accounts were frequently receiving Non-Delivery Reports (NDRs) featuring error code 0x80070005-0x0004dc-0x000524.
The glitch primarily affected users who had added an Outlook.com account to a profile that was already linked to another Exchange account. When these users tried to send or reply to emails, a pop-up error message would appear, advising them to try again later or contact their network administrator. Microsoft noted that the issue could also be triggered if the sender's account had a mail contact in Exchange Online with the same SMTP address.
Fix Now Fully Deployed
According to an update in the Outlook team’s support documentation, Microsoft completed the necessary server-side changes on April 3, 2026, and the fix is now live in the production environment.
For users still experiencing issues, Microsoft recommends switching to the "New Outlook" client or using the web version of Outlook.com to send emails. Additionally, the company provided a temporary workaround: users can manually download the Outlook Address Book for the affected Outlook.com account to bypass these permission-related errors.
This fix is part of Microsoft's ongoing maintenance efforts for Classic Outlook. Last month, the company addressed a client crash caused by the Microsoft Teams meeting add-in. Currently, Microsoft’s engineering teams are still investigating other known bugs, including a "cannot connect to server" error when creating groups in Classic Outlook, as well as an issue where the mouse cursor disappears for some users within Office applications.
In the meantime, Microsoft continues to address stability issues with Exchange Online access, which have caused intermittent email access problems for some mobile and macOS Outlook users over the past several weeks.
