can somebody hacking the printers or scanners in my network so that he can take all scanned papers to his email?
The modern multi-functional devices which can print, scan and email documents are often not designed with security in mind. This means they can be easily hacked which was shown several times. This includes unauthorized access to the configuration or unauthorized replacement of the firmware just be sending a special print job.
I make sure that the printer does not send copies of the scanned paper to another email?
A firewall around the networked printer might ensure that the typical protocols for sending email are not reachable by the printer or that only a specific mail server is reachable which accepts only selected target mail addresses. This makes information leakage not impossible but harder.