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.

While we’re continuing to work towards full remediation, affected users can upgrade to the latest market build of 16.76 or higher to receive the previously mentioned temporary workaround which should provide significant relief.

Current status: Our testing indicates that the previously mentioned method to bypass impact by updating to market build 16.76 or higher has reduced instances of impact by approximately 85 percent, but some impact is ongoing. We’ve completed our preparations for deployment of the supplemental code update which we anticipate will remediate the remaining impact, and we’ve initiated deployment to our internal testing environment to ensure efficacy before beginning deployment to the impacted service environment. Barring unforeseen obstacles, we anticipate that this validation will be complete by our next scheduled update, at which time we’ll begin full deployment of the 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: Monday, September 18, 2023, at 7:30 PM UTC