HP Multifunction Printer SMTP error

There were intermittent scanning to e-mail issues occurring with an HP Color LaserJet CM4540 MFP.  Initially, scan jobs of all sizes were having trouble going through.  There was an article found that suggested updating the firmware on the device.  After the firmware was updated, it seemed to correct issues with smaller scan jobs, but larger ones were still having issues.
When the scan jobs finished scanning the pages, the device would show on the display “SMTP Protocol Error”.  The e-mails would fail to go out.  During troubleshooting, the device could scan a 10 page document to e-mail (3 times successful), but not a color 46 page document (failed 3 times in a row). 
I tested setting the Exchange server’s hub transport settings from 10 MB to 40 MB.  E-mail sent successfully for the 46 page color scan 4 times with no problems.  What this proved was that the message size was too large to be sent through e-mail based on the e-mail size limit configured in Exchange.
If you happen to see “SMTP Protocol Error” message when trying to scan large documents, chances are the e-mail size is over the limit.

Networking multifunction HP SMTP