**Microsoft** has addressed a known issue that prevented some Classic **Outlook** users from sending emails using **Outlook.com** accounts. As previously reported, affected users encountered warnings indicating that some messages failed to reach recipients. ### Root Cause **Microsoft** identified that the issue primarily impacted users whose **Outlook.com** account was linked to another Exchange account within their **Outlook** profile. Users received non-delivery reports (NDRs) with 0x80070005-0x0004dc-0x000524 errors, displaying the message: "This message could not be sent. Try sending the message again later or contact your network administrator." **Microsoft** noted that these errors could also occur if the sender's account had an Exchange Online mail contact with the same SMTP address. %20error.jpg) *Classic Outlook non-delivery report error (Microsoft)* ### Resolution The **Outlook** Team announced that the problem was resolved with a server-side fix deployed on April 3, 2026. "The **Outlook** Team implemented a service change to address this issue that is in production as of April 3, 2026," **Microsoft** stated. ### Workarounds For users still experiencing email delivery problems, **Microsoft** recommends using the New **Outlook** client or **Outlook.com** on the web as alternative sending methods. Another temporary workaround involves downloading the **Outlook** Address Book for affected **Outlook.com** accounts, following the procedure detailed [here](https://support.microsoft.com/en-us/office/classic-outlook-error-when-sending-from-outlook-com-you-do-not-have-permission-to-send-on-behalf-of-the-specified-user-0x80070005-0x0004dc-0x000524-49f5afe9-11ee-4ce1-9531-296670171509#:~:text=Download%20the%20Outlook%20Address%20Book%20for%20any%20Outlook.com%20accounts%20that%20are%20having%20the%20issue). ### Other Ongoing Issues Recently, **Microsoft** addressed another Classic **Outlook** bug causing crashes when the **Microsoft Teams** Meeting Add-in was enabled. However, **Microsoft** is still investigating several other **Outlook** issues, including: * "Can't connect to the server" errors when creating groups. * A bug causing the mouse pointer to disappear in Classic **Outlook**, **OneNote**, and other **Microsoft 365** apps. * Ongoing **Exchange Online** issues intermittently preventing **Outlook** mobile and macOS users from accessing their mailboxes.