Winlink is a system that allows amateur radio operators to send email over the air from one radio station to another until a station that has Internet connectivity is available and the email is then sent out over normal Internet protocols.
In the event of an emergency or disaster where Internet connectivity is interrupted, Winlink can fill in the gap until normal service is restored. This doesn’t have to be a major disaster. An example is when a piece of heavy equipment cuts through a fiber optic cable causing interruption that can last days!