[Dovecot] Mailboxes separated from IMAP server

[Reymer Antonio Vargas Solano]

Hello folks,

 At my university we are trying to implement a distributed email backend,
but I have some troubles,

The topology:

Server A: Postfix+LMTP # MTA
Server B: Dovecot+LMTP # Just mailboxes
Server C: Dovecot # POP3/IMAP

Right now the Server A can leave a received email to the Server B, but I
don't know how to communicate Server C to the Server B to retrieve the
emails.

 I think that we should use IMAP protocol, but I am confused about how to
connect them, I don't know if we have to use a proxy IMAP server, or
another thing.

 Can anyone give me  an idea?

Regards,

Reymer Antonio Vargas Solano