Voicemail detection not working consistently on outbound calls

Support Help
1

Hi Retell team,

I’m reaching out because voicemail detection does not seem to be working reliably for one of our outbound voice agents.

We have voicemail detection enabled for the agent, but in multiple cases the call appears to have reached voicemail and was still processed as an unsuccessful call instead of being identified as voicemail.
From the actual call behavior and history on our side, this looks like a voicemail case that was not detected correctly.

I have screenshots showing:

1.⁠ ⁠the voice agent settings with voicemail detection enabled, and
2.⁠ ⁠the call history/examples where voicemail detection did not work as expected.

Could you please help clarify:

•⁠ ⁠what might cause voicemail detection to fail in cases like this,
•⁠ ⁠whether there are known limitations by carrier, region, or call flow,
•⁠ ⁠and what workarounds or best practices you recommend to improve voicemail detection reliability?

Also, if there are additional settings we should enable, such as any IVR-related handling or other call configuration changes, please let us know.

Happy to share the screenshots and any relevant call IDs or webhook payloads needed for investigation.

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2

Hi @business

Could you please provide a call ID where you experienced this issue? This will help us investigate more effectively.

Thank you!

3

Hi @shaw

call_57d76fad636467c3fdceea7af38

here is a call_id where I experienced this issue.

4

Hi @business

Thanks for reaching out and for sharing these details. I’ve escalated your issue to our team for further review.

We’ll keep you updated as soon as we have more information.

5

Hi @business your agent’s language is set to English (en-US), but the calls are going to Spanish phone numbers (+34). Voicemail detection relies on speech recognition to transcribe the voicemail greeting, and the English speech recognition model can’t properly transcribe Spanish greetings — it comes through as inaudible/unrecognized speech. Without a readable transcript, the voicemail classifier has no text to work with. If you’re calling both English and Spanish numbers, consider creating separate agents for each language, or use the Multi language setting.

Thank You