Quoting KT Walrus <ke...@my.walr.us>:

On Oct 12, 2016, at 2:07 PM, Rick Romero <ad...@vfemail.net> wrote:

Quoting KT Walrus <ke...@my.walr.us>:

I’m in the process of setting up a Dovecot IMAP proxy to handle a

of IMAP server domains. At the current time, I have my users divided
into 70 different groups of users (call them G1 to G70). I want each
group to configure their email client to access their mailboxes at a
domain name based on the group they belong to (e.g., g1.example.com
<http://g1.example.com/>, g2.example.com <http://g2.example.com/>, …,
g70.example.com <http://g70.example.com/>). I will only support TLS
encrypted IMAP connections to the Dovecot IMAP proxy (‘ssl=yes’ in

inet_listener). My SSL cert has alternate names for all 70 group domain

I want the group domain to only support users that have been assigned
the group the domain name represents. That is, a user assigned to G23
would only be allowed to configure their email client for the IMAP
server named g23.example.com <http://g23.example.com/>.

My solution during testing has been to have the Dovecot IMAP proxy to
listen on different ports: 9930-9999. I plan to purchase 70 IPs, one
each group, and redirect traffic on port 993 to the appropriate Dovecot
IMAP proxy port based on the IP I assign to the group domain name in
site’s DNS. The SQL for handling the IMAP login uses the port number
the inet_listener

I think this could work in production, but it will cost me extra to
the 70 IPs and might be a pain to manage. Eventually, I would like to
have over 5,000 groups so requiring an IP per group is less than ideal.
I also think having Dovecot IMAP proxy have 5,000 inet_listeners might
not work so well or might create too many threads/processes/ports to
on a small proxy server.

I would rather have 1 public IP for each Dovecot IMAP proxy and somehow
communicate to the userdb which group domain name was configured in the
email client so only the users assigned to this group can login with
that username.

Anyone have any ideas?

Do you have a SQL userdb?
Create a table or a 'host' field for the user.

user_query = SELECT CONCAT(pw_name, '@', pw_domain) AS user, "89" as
"89" as gid, host, 'Y' AS proxy_maybe, pw_dir as home, pw_dir as
CONCAT('maildir:', pw_dir , '/Maildir/' ) as mail_location FROM vpopmail
WHERE pw_name = '%n' AND pw_domain = '%d'

(mine is based on qmail/vpopmail)

Then populate 'host' for each user if you don't have any other way of
programatically determining the host..

This doesn’t solve my problem. Indeed, I am doing this already:

password_query = SELECT password, 'Y' as proxy,
CONCAT_WS('@',username,domain) AS destuser, pms AS host, ’secretmaster'
AS master, ’secretpass' AS pass FROM users WHERE username='%n' and
domain='%d' and (group_id=%{lport}-9930 or %{lport}=143 or '%s'='lmtp')
and mailbox_status='active’;

This is the password_query I am using on the Dovecot IMAP proxy. This
proxy doesn’t use a user_query (only the real backend Dovecot servers
do). I allow authorizations on port 143 only for Postfix. Port 143
exposed to the email clients (only 993 is used by email clients).

Anyway, checking the %{lport} allows only IMAP logins using the proper
domain name (IP or port) to allow the log in of the user.

I’m looking to find out the IMAP server name that the user configured
their email client with and make sure I only allow users to access their
mailboxes using their assigned IMAP server name.

Note that the problem I am trying to solve is if the user configures
their email client with the wrong IMAP server name (e.g. using
g2.example.com <http://g2.example.com/> instead of g23.example.com
<http://g23.example.com/>) and later I move G23 to another datacenter
and leave G2 in the current datacenter, they will not be able to access
their emails since the G2 datacenter doesn’t have their mailboxes any
more and the mailboxes for G23 are only in the G23 datacenter. My users
aren’t email experts and I don’t want them to have to discover that
made a typo in the original setup long after they have forgotten how
they set up the client in the first place.

To start with, the mailboxes will all be in the same datacenter, but I
want to be able to move some of the mailboxes to be geographically
closer to the users of those mailboxes (like Western users using Western
servers while Eastern users use a datacenter closer to the East coast).

Gotcha.  I used g1.example.com and g2.example.com.   There are some DNS
services that will provide unique records based on the region of the caller
- but I have no experience with those.  That's what I'd prefer to do in
the long run though.

In my setup, the 'host' field still has the internal IP of the servers
physically hosting mail at g1 and g2 in order to allow the user to connect
to g1 and still be redirected to g2 ('internally' via VPN) until they
manually change the mail server name in their client.  It also allows
seamless migrations.
All I need to be concerned with is database replication.


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