Microsoft are aware Users may be intermittently unable to access their Exchange Online mailboxes in some connection methods.
More info
This issue may intermittently impact some users attempting to access the Exchange Online service through the Outlook mobile apps or the new Outlook for Mac desktop client.
Scope of impact
This issue intermittently impacts some users attempting to access their Exchange Online mailboxes, with a smaller subset of users persistently unable to access their Exchange Online mailboxes in the Outlook mobile apps or the new Outlook for Mac desktop client. This section may be updated as our investigation progresses.
