Oki CX2731MFP Advance User Manual page 76

Note
This function is only for scanning. Internet faxing cannot be
used.
1 On the [Scan Menu] screen (press the <Scan> key), select the
scan mode you want, then press <OK>. If you select
[USBmemory], skip step 2.
2 Press the down arrow key to select [Scan setting], then press
<OK>.
3 Press the down arrow key to select the [Grayscale], then press
<OK>.
4 Press the down arrow key to select [ON], then press <OK>.
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MC361/MC561/CX2731 MFP Advanced User's Guide
– Scanning: Scanning and Internet Faxing