How to organize a mail exchange for several users with one external mailbox?

Question

Email

Office, 10 working PCs, peer-to-peer network, the gateway is an ADSL modem, which also distributes the Internet.
All work with one external mailbox on @mail.ru. MS Office mail client, POP3 connection. Every day, about 10-15 letters with large attachments arrive. The channel is not stable, the speed is about 64 k, the provider's traffic is running at 1.5r / mb, and a rather large amount accumulates in a month. The challenge was to reduce communication costs.
I am considering this option - to build a local server that will download all letters from an external mailbox. Clients will download emails already from the local server.
I have never encountered such problems, and therefore I ask for help in resolving this issue. How to implement this scheme, what software? Can you advise other options, I will be grateful for any suggestions.

Answer 1

as an option, work with a dynamic mail archive. the server (an ordinary MS outlook client configured differently) pumps out all mail (POP or just a local data file) into a data file, which the user then clings to over the network.
*Never used in practice

Answer 2

There is a solution for *nix - Fetchmail and its manual in Russian