Winlink Global Radio Email®️ “…is a network of amateur radio and authorised government stations that provide worldwide radio email using radio pathways where the internet is not present. The system is built, operated and administered entirely by licensed Radio Amateur volunteers. It supports email with attachments, position reporting, weather and information bulletins, and is well-known for its role in interoperable emergency and disaster relief communications. It is capable of operating completely without the internet–automatically–using smart-network radio relays. “
Wave Talkers have produced a good set of videos that cover the basics of Winlink which can be found in their YouTube playlist
Winlink (Wikipedia) can use AX.25, ARDOP, VARA HF, VARA FM, PACTOR Telnet for networking. Telnet is by far the easiest method to start out with, once mails are being exchanged then moving to RF is the best option. Application software is available for Windows, Mac, Linux, and Android with Pat being a cross platform compatible programme.
Once setup these are some of the things you might do: