Why does DTMF from outside sources trigger automated systems when calling from a cell phone/VOIP to other numbers, but not your own voicemail?

[s355]

I can use Voicemeeter+Bluetooth Audio Receiver to transmit the sound of the ToneDef app on my phone over the PC's microphone. The service used is Google Voice.

 

[hotaru.hino]

Let me make sure I understand what you're getting at based on the question:

• There's a DTMF tone source from outside, I'm guessing you mean someone is calling you and providing you DTMF tones.
• The DTMF tones are supposed to trigger automated functions you've set up
• This works when the DTMF is sent from a source that called you from either normal phone dialing or VoIP
• This does not work when someone leaves a voice mail that has DTMF tones, and you're playing the voice mail into your system