[Dovecot] Dovecot on different server than MTA

[FORMER 03 | Baltasar Cevc]

Hi,

I'm setting up our new mail system using dovecot as mailbox server. As
our goal is to have many many small redundant (virtual) servers as
components, for example a mailhub (just relaying mail) and a frontend
smtp server (just accepting or denying mail in the first place and
then forwarding it to the mailhub), etc. I want to run Dovecot on a
different server than the main MTAs. The mailbox server is the only
service that cannot be made redundant in an easy way (the servers
don't have common storage and we can't add that easily), thus I prefer
not to have it on the same server as the relay.

Is there a best practice to do that? My current ideas are either to
implement a stripped-down Postfix in the Dovecot server or to use some
qpsmtpd setup there, both just to call the Dovecot delivery program.
SMTP will be the communication protocol for the components except
dovecot. (e.g. the virus scanner will be implemented as SMTP proxy).

I'm quite bad at ASCII art, but I'll try anyways to illustrate the
setup:

I <--> [public incoming MX] -------------\
N                                        |
T                                       \|/
E <--> [customer mailrelay] -----> [Postfix Mailhub] <====> virusscanner
R                                    |   |
N <-------outgoing mails-------------/   |
E                                        |
T <--> [dovecot mailstore] <-mail delivery

Each of the subsystems will be on a different virtual server in order
to have small systems with distinct functions and to improve
scalability. Everything except the dovecot server is planned to be
duplicated on two different hardware machines (e.g. mx-in1 on server1,
mx-in2 on server 2, mailhub1 on server1, mailhub2 on server2,
virusscanner on server 2 and 3, etc. or something similar).

Thanx,
Baltasar

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