Microsoft is investigating and working to resolve Exchange Online mailbox access issues that have intermittently affected Outlook mobile and macOS users for weeks.

When it first acknowledged this service issue (tracked under EX1256020) last week, Microsoft said it started on March 11 and that the root cause was a newly introduced virtual account. While the company flagged it as resolved on April 1, the incident has been re-added to the admin message center under a different tag (EX1268771).

“We’ve received reports from affected tenants that the impact scenario originally communicated through SHD EX1256020 is still ongoing. We’re working to restart the Notification Broker service on affected portions of Exchange Online service infrastructure to remediate impact while we continue our analysis into the underlying root cause,” Microsoft says.