Microsoft Outlook.com outage blocks email attachments

Microsoft’s Outlook.com service suffered a widespread outage on Saturday, with error code 550 5.7.520 preventing the delivery of emails that contain file attachments. The disruption affected both corporate and private users in Germany and prompted Microsoft to advise sending files via OneDrive links as a temporary workaround.

The incident follows a series of recent Outlook problems, including login failures, IMAP/SMTP synchronization errors, and calendar update glitches reported in late July and early August. At the same time, security researchers disclosed a sophisticated campaign by the Russian‑linked “Laundry Bear” (also known as TA488) group that exploits the CVE‑2026‑42897 cross‑site‑scripting flaw in Exchange Server and Outlook Web Access. The attackers use the vulnerability to install the OWAReaper backdoor, targeting government agencies, telecom firms, financial institutions, and aerospace companies in the United States and Europe. Microsoft had previously released mitigations for the flaw in May and June.