[CentOS] Large scale Postfix/Cyrus email system for 100,000+ users

mouss mlist.only at free.fr
Tue Oct 23 15:29:45 UTC 2007

Matt Shields wrote:
> I'm trying to set up a large scale email system that supports 100,000+
> IMAP accounts.  We have an existing frontend web interface that does a
> lookup on a mysql db to figure out which IMAP server to connect to for
> each user.  For the email infrastructure we have decided on Postfix
> and Cyrus.  We have configured both to use mysql to get the virtual
> user information.
> Because of the way that the infrastructure is (biz reasons) we are not
> doing shared storage, we have numerous IMAP servers that we distribute
> accounts across.  As we add more users, we image up a new IMAP server.
>  For our business's scaling purposes this was the best plan.
> What I am having a problem is how do I get postfix to transfer the
> email to the particular IMAP server that the user account is on.  I
> know that I need to use lmtp and transport, but all the examples I
> have seen show forwarding all email to 1 IMAP server.  I would like
> Postfix to do a lookup for each mailbox and determine which IMAP
> server to deliver it to.

There are primarily two ways:

[virtual aliase]
you can use virtual_alias_maps to redirect foo at example.com to
foo at hostN.example.com, provided the final server accepts such addresses.

If the final server doesn't accept these, and you use smtp to relay to,
then you can write the addresses back, using smtp_generic_maps.

an laternative is to use use (per-user) transport_maps. something like

foo at example.com		relay:[hostN.example.com]

In bothe approaches, the mappings can be generated using sql statements
(mostly CONCAT). something like
query = SELECT concat('relay:[', host, '.example.com]')
	FROM User
	where '%u' = user and '%d' = domain

you get the idea I hope.

> Anyone have a working example that they could share?  It would be
> greatly appreciated.
> thanks
> -matt
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