host selection for services, database field

[runout-at]

i'd like to have a new feature which would make it easier to switch services between servers and make migration easier.
The server/service could retrieve a 'host' field from the database to decide if the domain belongs to it.
I suggest to have different 'host' fields for different services: smtp, imap, pop

Dovecot has such a feature for its proxy: http://wiki2.dovecot.org/PasswordDatabase/ExtraFields/Proxy

Database fields:

ALTER TABLE `maildb_vexim2`.`domainalias` 
ADD COLUMN `host_smtp` VARCHAR(64) NULL DEFAULT 'mail' COMMENT '' AFTER `alias`,
ADD COLUMN `host_imap` VARCHAR(64) NULL DEFAULT 'mail' COMMENT '' AFTER `host_smtp`,
ADD COLUMN `host_pop` VARCHAR(64) NULL DEFAULT 'mail' COMMENT '' AFTER `host_imap`;

Changes in vexim:

for virtual users
/etc/exim4/conf.d/main/00_vexim_listmacrosdefs

### main/00_vexim_listmacrosdefs
#################################

# if you exim version < 4.83 , define macro below for enabling new
# 'headers_remove' behavior. See https://github.com/vexim/vexim2/pull/102 .
#OLD_HEADERS_REMOVE = yes

#hide mysql_servers = localhost::(/var/run/mysqld/mysqld.sock)/vexim/vexim/CHANGE

# domains
VEXIM_VIRTUAL_DOMAINS = SELECT DISTINCT domain FROM domains WHERE type = 'local' AND enabled = '1' AND domain = '${quote_mysql:$domain}' AND host_smtp = 'mail'
VEXIM_RELAY_DOMAINS = SELECT DISTINCT domain FROM domains WHERE type = 'relay'  AND domain = '${quote_mysql:$domain}' AND host_smtp = 'mail'
VEXIM_ALIAS_DOMAINS = SELECT DISTINCT alias FROM domainalias WHERE alias = '${quote_mysql:$domain}' AND host_smtp = 'mail'

# domains and relay networks
MAIN_LOCAL_DOMAINS = MAIN_LOCAL_DOMAINS : ${lookup mysql{VEXIM_VIRTUAL_DOMAINS}} : ${lookup mysql{VEXIM_ALIAS_DOMAINS}}
MAIN_RELAY_TO_DOMAINS = MAIN_RELAY_TO_DOMAINS : ${lookup mysql{VEXIM_RELAY_DOMAINS}}

# primary hostname
#MAIN_HARDCODE_PRIMARY_HOSTNAME=myhostname

# add vexim system user
#MAIN_TRUSTED_USERS = www-data

# enable TLS
#MAIN_TLS_ENABLE = true

# enable av scanner
#av_scanner = clamd:/var/run/clamav/clamd.ctl

# use spamassassing
#spamd_address = 127.0.0.1 783

# validation of sending mailserver
#CHECK_RCPT_REVERSE_DNS = true
#CHECK_RCPT_SPF = true

# If the local-part suffix is used, mails to user+whatevertext@example.org will be delivered to user@example.org
# Comment this line if you want to disable it, instead of + you can use a different separator.
VEXIM_LOCALPART_SUFFIX = +*

CHECK_RCPT_LOCAL_ACL_FILE = /etc/exim4/vexim-acl-check-rcpt.conf
CHECK_DATA_LOCAL_ACL_FILE = /etc/exim4/vexim-acl-check-content.conf

for mailman i create subdomains 'lists.*' and have a config for that:
/etc/exim4/conf.d/main/00_mailman

# Home dir for your Mailman installation -- aka Mailman's prefix
# directory.
MAILMAN_HOME=/var/lib/mailman
MAILMAN_WRAP=MAILMAN_HOME/mail/mailman

# User and group for Mailman, should match your --with-mail-gid
# switch to Mailman's configure script.
MAILMAN_USER=list
MAILMAN_GROUP=daemon
#MY_IP=x.x.x.x

MM_DOMAINS = SELECT DISTINCT domain FROM domains WHERE type = 'local' AND enabled = '1' AND domain LIKE 'lists.%' AND domain = '${quote_mysql:$domain}' AND host_smtp = 'mail'
domainlist mm_domains=${lookup mysql{MM_DOMAINS}}
MAILMAN_LISTCHK=MAILMAN_HOME/lists/${lc::$local_part}/config.pck

[Udera]

There are too many changes for the current release.

Do you just want to run a separate smtp and imap server or do you really want to put a feature for clusters? For a cluster you would probably sync the databases and in that case it wouldn't make sense to hardcode the hostname mail.

Currently it looks more like a feature to turn smtp, imap and pop on and off.

[runout-at]

sorry, i mixed some commits into one. this was not the plan and i don't know if it's possible to split the commits.

it would be great to fix the quota bug.
and to get the domainguess feature soon

The host selection for services feature needs some more documentation and i will provide examples for exim and dovecot. The example of my original post was just a first idea and has improved a lot with more complex SQL queries and an additional router for exim and a SQL query for dovecot to be a proxy for some domains.

mail is not really a hostname. it can be anything so the service can decide if it is responsible to handle this mail/domain. Maybe i should not use mail which is confusing.
In my actual case i use it for migration purposes to tell the new server to be a proxy for a domain (or not). This way i can change DNS records without waiting until they time out. And have a minimal downtime during sync of the file system and then just change the host_smtp and host_imap fields in the vexim-db.
I think there are some other use cases for this feature like load balancing and clustering.

[Udera]

For the quota, I would prefer the version from Exim4U (#133 (comment)) since with your version you could end up with a single M if the extraction-pattern doesn't work. Just create a new pull request for the quota problem, then I can merge it soon.