Why does the user always hear the prompt that”The number you dialed cannot be reached now, please leave the message after the tone” when calling a specific extension?

Why does the user always hear the prompt that”The number you dialed cannot be reached now, please leave the message after the tone” when calling a specific extension?
The problem might result from one of the following configurations:

1. The extension has been set up “always transfer to voicemail”; the user can log in “User Web Interface” and uncheck the “always transfer to voicemail” option.
2. The extension or the phone has enabled “DND” function.

• If it is the extension that enables”DND”, then it can be canceled by entering the feature code (the default value is”
  *075

  ”) on the phone. Also the user could log in “User Web Interface”, select “Settings” and uncheck the DND option.
• If it is the phone that enables “DND” function, and you can see the “DND” on the phone screen, please cancel the “DND” function according to User Manual of the phone.