Yealink SIP-T4X Administration Manual page 96

Configuring Basic Features
2) (Optional.) Enter the DND on code in the DND On Code field.
3) (Optional.) Enter the DND off code in the DND Off Code field.
b) If you mark the Custom radio box:
1) Select the desired account from the pull-down list of Account.
2) Mark the desired value in the DND Status field.
3) (Optional.) Enter the DND on code in the DND On Code field.
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