[1] Usually, it involves digital data being transformed into physical letter items at distributed print centres located as close as possible to the final delivery addresses.
The system was invented by UK company CFH, who launched their Hybrid Mail solution Docmail in 2008.
Generally there is a fee for this service; however very small amounts and single email letters may be free of charge depending on the service provider and generally fees are much lower than cost incurred in sending the mail directly or by using a franking machine.
[3] There are also reverse systems, where handwritten letters can be delivered as email.
However, special care must be taken to inspect local laws and the service provider's scanning practices to ensure that they are not reading the mail or acting on behalf of the client from a legal standpoint.