u/gnon17

I have a client that started intermitently not receiving voicemails for their Teams phone system. All was working fine for years until a few weeks ago. For every 10 test voicemails we leave, maybe 1 or 2 show are delivered as a voicemail (in the teams app and their mailbox). This is occuring for both users and shared group mailboxes. I have a Microsoft Case opened, but they've been slow. Wondering if anyone else has every experienced this? Things we have tried and additional information:

• Verified tenant/users are properly licensed (M365 Business Premium + Teams Phone Standard + Caling plan PAYG + communication credits)
  • I typically recommend the Teams Phone + Calling plan bundle, but I am not the CSP for this client and inherited this licensing. This is the only difference between my other tenants where things are working, but this shouldn't affect voicemail.
• Checked message trace in Exchange Online and confirmed that email security is not preventing the voicemail emails from being delivered. They don't even show up in message trace.
• No recent changes to the phone system settings or exchange
• Voicemail is enabled for all users
• Users receive the call and missed call notifications
• All test voicemails we leave are at least 5 seconds long.
• Tried swapping phone numbers
• Rebuilt auto-attendant and shared group mailbox
• Verified the calls show up in the PSTN usage reports

I've never had this issue and have had clients using Teams Voice for 5+ years. Microsoft also seems to have no idea on this. Hoping someone has seen this before. Thanks.