Resolved -
There has been a significant reduction in the number of failures for Office 365 requests with attachments larger than 3 MB. We will continue to monitor.
Apr 22, 21:56 UTC
Update -
Office 365 servers may sometimes fail to accept attachments larger than 3 MB. As a temporary alternative, we suggest using another method of sharing files with recipients, such as OneDrive. We have communicated the issue to Microsoft and are investigating additional mitigations.
Apr 17, 18:47 UTC
Investigating -
We received reports from a small number of customers that some drafts error when sending, with the message:
"Unexpected problem sending attachment larger than 3MB to Office 365."
Apr 17, 13:15 UTC