The development of this email service has conceptual variations that are dominated by two-party scenarios with only one sender and one receiver as well as a trusted third party (TTP) serving as a mediator.
As in traditional registered mail, many certified email technologies call for the parties involved to trust the TTP, or the "postman", because it has the capacity to reveal the identity of the sender to the recipient once the protocol is initiated.
[7] There are, however, some applications based on multi-party email protocols; these include the technology originally proposed by Markowitch and Kremer, that involves an online or offline TTP in addition to the sender and receiver.
Some applications also offer add-in features, such as the integration of the concept of timeliness, wherein a participant to the process can terminate a session in finite time in order to avoid waiting for a reply forever.
Since July 1 of 2013, all communications between enterprises and the Italian public administration are required to be sent through PEC and paper documents are no longer accepted.