Microsoft fixes Outlook email sending issue for users with many folders

Microsoft is rolling out fixes for an Outlook for Microsoft 365 issue that generates NDRs (0x80040305) when sending emails from accounts with too many nested folders (~500+), now affecting primary mailboxes in addition to previously addressed shared folders. The fix is scheduled across Beta, Current Channel Preview, Current Channel (Oct 2024), and Monthly Enterprise Channel (Dec 2024). Interim workarounds include reducing nested folders below 500 (target ~450), keeping folders collapsed, avoiding certain online actions (e.g., View on Server, Include older results), and restarting Outlook after such actions; related stability issues in Microsoft 365 apps are also noted.