Jan 18, 2014

Mail server migration

Goal

Migrating a mail server from one server (FreeBSD physical server) to another one (Debian virtual machine) without loosing mails.

Mail server

Retrieving mails from other email providers

  • fetchmail (cron)
crontab -e
*/3 * * * * $HOME/bin/getmymailnow > /dev/null

~/bin/getmymailnow:

#!/bin/sh
LOCKFILE="$0.lock"
PATH="/bin:/usr/bin"

if [ -f "$LOCKFILE" ]; then
  PID=$(cat "$LOCKFILE")
  if ! ps $PID 2> /dev/null; then
    echo "Ignoring stalled lock file" >&2
  else
    echo "Script already running (PID=$PID)" >&2
    exit 1
  fi
fi

fetchmail -a -s -m "procmail -d %T" 2>&1

echo $! > $LOCKFILE
wait
rm "$LOCKFILE"

exit 0

Tools used for local/virtual mail handling

  • Postfix
  • Dovecot
  • Spamassassin
  • roundcube
  • procmail
  • fetchmail
  • bind

Initial step

  • Create required users on new server

  • Configure postfix on new server as it was on old one

    • remove mail domain from mydestination to old server
    • set relayhost to old server

  • If different domain should be relayed to different places:

transport_maps = hash:/etc/postfix/transport_maps

domain.tld smtp:[mail.plop.tld]

postmap /etc/postfix/transport_maps
service postfix restart
  • Update MX in DNS conf to use new server

All mails should now go to new server, and this one will relay mails to old server.

  • Install dovecot on new server
  • Migrate and update conf, see upgrading dovecot
  • Migrate/update required certificates
  • Make an initial copy of the mailstores to the new server using rsync
rsync -avz --stats ~plop/Maildir -e ssh plop@new.server.tld:
  • Validates that imap/dovecot is working as expected
openssl s_client -connect new.server.tld:993
a01 login plop the_PassWord
a02 SELECT INBOX
a03 logout

  • Copy spamassassin conf (global/local) to new server (and review it)

  • Copy procmailconf to new server (and review it)

  • Copy fetchmail conf (global/local) to new server (and review it)

  • Install postgresql on new server

  • Migrate roundcube postgres database/user

    • Database dump have to be updated as postgres user name is different
sed -i 's/pgsql/postgres/g' roundcube.sql

  • Install roundcube on new server

  • Update roundcube conf

  • Validate that roundcube is working as expected

  • Wait at least a week to ensure that DNS will be up-to-date with new MX (and check that you have a small DNS TTL)

  • Update DNS entries for SPF

Final step - including small downtime

  • Stops email fetching on old server
  • Stops postfix on old server
  • Stops dovecot on old server
  • Stops roundcube vhost on old server
  • Make an incremental copy of the mailstores, deleting no more present emails using rsync
rsync -avz --delete-after --stats ~plop/Maildir -e ssh plop@new.server.tld:
  • Configure postfix on new server:
    • disable relaying to old server
    • fix mydestination
  • Switch IPs (or hostnames if not possible) to new server
  • Update required hostnames in new server
  • Update roundcube postgres database
  • Enable email fetching on new server
  • Configure postfix on old server to relay mails to new server
  • Clean old server
  • Clean DNS conf

No emails should be lost as if the server is not available, the contacting servers should hold and resend the mails.