Winlink is a worldwide radio email service that uses amateur-band radio pathways where the internet is not present and is capable of operating completely without the internet
This system can get messages through where even voice is not practical to use, as it uses a store and forward system which routes using radio. It is similar to the way normal e-mail would forward automatically across the Internet choosing the best route around any problems. Winlink does the same but via radio pathways.
More complex (and accurate) messages can be composed and then only require a few retries and short throughputs to get the message transmitted, and it can be retrieved in the same manner. This is ideal for say maritime vessels which may only get sporadic periods of communication but where they can in that time transmit and receive any messages.
Message services can include email with attachments, position reporting, weather bulletins, emergency and relief communications, and message relay.
Typically if an area is hit by a disaster and normal communications are down, an amateur radio operator with this service could send emails to any normal Internet address elsewhere in the world, and receive messages back.
End-user software used could be Winlink Express for Windows or Pat (cross-platform) and there are other choices too.