Some users’ email with attachments sent from Outlook for Mac may be delivered without attachments

Title: Some users’ email with attachments sent from Outlook for Mac may be delivered without attachments

User impact: Users’ email with attachments sent from Outlook for Mac may be delivered without attachments.

More info: Users can verify if they’ve encountered this problem in Outlook for Mac by reviewing their Sent Items to validate if a sent message contains an attachment. If users don’t see the attachment, they can reply to the message in their Sent Items folder to reattach and send the message again.

Current status: We’ve deployed a fix to update attachment logic that we’ve confirmed will reduce instances of this issue from occurring when users frequently add and remove attachments by 40 percent. Our development of a long-term solution to this problem is contingent on the telemetry we’re collecting subsequent to the delivery of our attachment logic update, and we’ll provide a better estimation on the development of the long-term fix when available.

Scope of impact: This issue is specific to a very small percentage of users’ email with attachments sent from Outlook for Mac.

Start time: Monday, July 10, 2023, at 8:08 PM UTC

Root cause: A conflict occurring with how our service detects attachment IDs before sending email in Outlook for Mac is resulting in the service removing attachments on sending email.

Next update by: Wednesday September 27, 2023, at 7:00 PM UTC