HPLIP software is not used in support of scanning on certain multifunction products (MFP's), some of which are listed below.  These products which use HP Digital Sending Technology allow scanning directly to email addresses, network folders, or other networked devices.
 
These MFP's do not support the SANE or TWAIN APIs, so HPLIP which provides SANE support is not needed for these devices.

Some Hewlett-Packard MFP's that use Digital Sending Technology:

HP LaserJet M3035mfp
HP LaserJet 4100/4101MFP
HP LaserJet 4345mfp
HP LaserJet M4345MFP
HP LaserJet M5035mfp
HP LaserJet 8000/8100/8150MFP
HP LaserJet 9000/9000L MFP
HP LaserJet 9040/9050MFP
HP LaserJet 9055/9065 MFP

HP Color LaserJet 9500MFP
HP Color LaserJet 4730MFP
HP Color LaserJet CM4730mfp

CM8050/8060 Color MFP with Edgeline Technology

( An MFP that supports Digital Sending has "DS" noted in its Scan column on the Supported Products/Models page).