We are actively investigating an issue resulting in intermittent delivery failures when sending to external recipients.
While measures are being taken to prevent any impact to users, some may experience mail delivery delays or delivery failures. Impacted users are encouraged to retry their messages.
We are aware of duplicate messages occurring in the Outlook Desktop client when using a POP3 connection. We are still investigating this issue as users are not seeing duplicates in Webmail, Thunderbird, or Apple Mail. We are continuing to collect examples and are monitoring Microsoft's status page.