Using classic Outlook for Windows in business environments
Hi @Bradley
In this situation, I would recommend consulting the Mitel support team first to better understand the configuration and integration on their side. Since this forum primarily focuses on Microsoft 365 technologies, and the scenario involves a third -party solution, it may be difficult for community members to provide detailed guidance without access to a similar environment.
In addition, you may consider running a message trace to identify the source IP address and determine which mailbox sent the voicemail message to the recipient.
For more details, please refer to the following article: Message trace in the new EAC in Exchange Online | Microsoft Learn
I hope this helps point you in the right direction for your investigation.
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