Normal e-mail communication without extra safety measures is regarded as an insecure medium, because messages can be read and optionally modified by a third party.
Most of the e-mail programs already support the so-called X.509 certificate and the secure protocol, S/MIME. Every Fraunhofer employee has such a certificate as his/her digital proof of identity, so that you can communicate with them in a secure way. For communication with Fraunhofer employees, outsiders can get a free certificate. How this can be done is described on this website.