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 determined that the immediate fix to update attachment logic to reduce instances of this issue from occurring needs to be deployed incrementally at a monitored pace to ensure it successfully remediates impact without adversely impacting other aspects of the service. We’ve initiated the deployment and anticipate it will reach the affected users by mid-October 2023. We’ll aim to provide a precise completion date once one becomes available. Furthermore, the immediate fix will reduce the probability of the issue consistently occurring, though a secondary long-term fix will need to be developed in order to fully resolve the underlining issue and remediate impact. We’ll continue to provide updates on the long-term fix alongside the deployment updates for the initial fix.

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 October 4, 2023, at 7:00 PM UTC