How to collect, store and share email on a local server?

Question

css

For certain incorrectly formulated request, but an essence in the following. There are several mail accounts for the Yandex domain. It is necessary to collect and store it all and entirely on a server locally located in the enterprise network, so that mail clients can access it, bypassing the Yandex MDA. Synchronization between Yandex and this local server must take place via IMAP, because the entire existing subfolder structure will go with the POP3 forest. Such an intermediate server (again, how to call it correctly? relay server?) will not perform any other tasks, outgoing messages will be sent through the most ordinary smtp.yandex.ru.
What are the common options for implementing such a scheme?

Answer 1

jsfiddle.net/soledar10/3g7d5ne5
or
jsfiddle.net/soledar10/1jw88vga

Answer 2

Fundamentally
1. The server with external and internal interfaces is mutated
2. initially, the mailbox tree will have to be synchronized (imapsync), further mail sync using fetchmail
3. there must be a dns server in the local network where the internal zone must be configured by the same name as external. that is, for internal clients, ping mail.domain.tld should give the internal address of your server
4. Yandex mx's are indicated in the same internal zone so that clients can send. It is a monstrosity to indicate external addresses in the internal zone, but without this your task cannot be
solved