The Canon iR5000i digital printer (and probably other imageRunner models)
has a somewhat undocumented print-from-email feature.

Any text/plain email sent to port 25 on the device will be printed.
The MAIL FROM and RCPT TO values are not authenticated or even checked
for syntax.

There appears to be no way to disable email printing via the Web interface
or front panel, as there is for lpd, ipp and http printing.

Recently these printers have been targetted by spammers as an apparent
open relay (if they don't bother to test for forwarding). There is thus an
effective DoS attack by paper consumption.

This service is blocked by the provided ip address range filtering option.

-- 
Andrew Daviel, TRIUMF, Canada
Tel. +1 (604) 222-7376
security@triumf.ca