Outlook group .mp3 attachments not shown in outlook classic

Microsoft has identified a product regression that matches the reported behavior under Bug ID 12322662: "VoicemailPlayerV2 Integration Hides MP3 Files Even When Feature Off."

• The issue has been investigated by the Product Group, and a fix has already been developed.
• Based on the current release cadence, it is anticipated to become available in the Current Channel with an upcoming update – mid of October 2026.

Hello Thomas de Haan,

Based on my research, several other users have reported similar behavior where an .mp3 voicemail attachment is visible in New Outlook and Outlook on the web but does not appear in Classic Outlook.

A related discussion is available here: Audio.mp3 is not displaying in Classic Outlook for desktop | Microsoft Q&A

In particular, please refer to the response posted by Brent Douglas, who shared a detailed explanation of the behavior and the workaround that was successfully tested in their environment.

• For voicemail messages that have already been delivered, forwarding the message to yourself may cause the .mp3 attachment to appear normally in the newly received copy.
• For new voicemail messages, Brent Douglas reported success by using an Exchange Online mail flow rule to remove the Content-Class: voice header before the message reaches the mailbox. This allows Classic Outlook to process the voicemail as a regular email and display the .mp3 file as a standard attachment.

Since the PowerShell approach changes how voicemail messages are processed, please ask your organization’s IT administrator to review and test it in a limited environment before making any production changes. The administrator should also consider whether the change could affect voicemail transcription, retention policies, compliance searches, or other voicemail functionality.

Please note that this mail flow rule would only affect new messages. Voicemails that have already been delivered would retain their existing message classification, so forwarding them to yourself would remain the available workaround.

At the same time, I recommend asking your IT administrator to open a support ticket with Microsoft through the Microsoft 365 Admin Center. A Microsoft Support agent can collect the relevant Outlook and message diagnostic information, confirm whether the behavior is associated with the current Classic Outlook build, and review the appropriate next steps: Get support - Microsoft 365 admin | Microsoft Learn

Until then, users can continue accessing the original .mp3 attachments through New Outlook or Outlook on the web. For previously delivered messages, forwarding the voicemail to yourself can be used as a temporary workaround.

Kind regards,