1. Edit /etc/postfix/virtual This is a plaintext file where you can specify the domains and users to accept mail for. Each virtual domain should begin with a single line containing the domain name. The subsequent lines define addresses at the domain that are deliverable. Mail will be delivered to local usernames on the right side, as demonstrated in the example below. The condition @domain allows you to deliver “all other” mail to the indicated user. You can list multiple domains in this file; just repeat the format demonstrated below.

example.com		this-text-is-ignored
postmaster@example.com	postmaster
address1@example.com	destuser1
address2@example.com	destuser2
@example.com		destuser1

2. Edit /etc/postfix/main.cf

You have to tell postfix where to look for these virtual alias mappings; the appropriate configuration directive is in the main postfix configuration file. This tells postfix to use the db-format (hash) version of your virtual mappings. Note that your system must have db support for this to work; also, the actual db file is not created until you run ‘postmap’ in step 3.

virtual_alias_maps = hash:/etc/postfix/virtual

3. Refresh configuration and mappings

Since you’ve changed main.cf, you should restart the daemon. The second command below updates the virtual mappings; you must run this ‘postmap’ command when you change your /etc/postfix/virtual file. The ‘postmap’ command actually creates the hash db file that postfix looks for.

postfix reload
postmap /etc/postfix/virtual

Now try delivering mail to virtual domain addresses. If you encounter problems, check your mailer daemon system log and make sure your server configuration has been refreshed with ‘postfix reload’ and the ‘postmap’ commands.

When Postfix does not receive or deliver mail, the first order of business is to look for errors that prevent Postfix from working properly:

% egrep '(warning|error|fatal|panic):' /some/log/file | more

Note: the most important message is near the BEGINNING of the output. Error messages that come later are less useful.

The nature of each problem is indicated as follows:

• “panic” indicates a problem in the software itself that only a programmer can fix. Postfix cannot proceed until this is fixed.
• “fatal” is the result of missing files, incorrect permissions, incorrect configuration file settings that you can fix. Postfix cannot proceed until this is fixed.
• “error” reports an error condition. For safety reasons, a Postfix process will terminate when more than 13 of these happen.
• “warning” indicates a non-fatal error. These are problems that you may not be able to fix (such as a broken DNS server elsewhere on the network) but may also indicate local configuration errors that could become a problem later.

/etc/postfix/master.cf:    smtp      inet  n       -       n       -       -       smtpd -v

To diagnose problems with address rewriting specify a “-v” option for the cleanup(8) and/or trivial-rewrite(8) daemon, and to diagnose problems with mail delivery specify a “-v” option for the qmgr(8) or oqmgr(8) queue manager, or for the lmtp(8), local(8), pipe(8), smtp(8), or virtual(8) delivery agent.

openssl req -new -x509 -nodes -days 365 -out cert.crt -keyout cert.key
cat cert.key cert.crt > cert.pem

Endre navnet på filene slik at de stemmer overns med configfilene til de respektive programmene.

While the script is rather simple, it can save a fair bit of typing when migrating some hundreds of mail accounts, especially since Courier stores some of its own state files recursively in each folder of the maildir hierarchy, making it a real pain to otherwise manually rename or remove all of them.

Here’s a plain-English summary of what the script currently does, when given a Courier maildir path as an argument:

• Check that the given path is indeed a valid Courier maildir, and exit if not.
• Rename the file ‘courierimapsubscribed’ to ‘subscriptions’, and strip the ‘INBOX.’ prefix from its contents.
• Recursively rename all of files of the name ‘courierimapuiddb’ to ‘dovecot-uidlist’.
• Recursively delete all of files of the name ‘courierimaphieracl’, ‘courierimapacl’ and ‘courierimapkeywords’.

The script will also verbosely print out each action it performs, handy for redirecting the output to a log file for a large migration.

Hopefully people about to jump ship from Courier to Dovecot find this useful. If anyone comes up with improvements to the script, please send them my way.

#!/bin/sh
#
# courier2dovecot -- Converts a Courier maildir to Dovecot format.
# Copyright (c) 2005 Arto Bendiken. Released under the GNU GPL.
# Newest version available from http://bendiken.net/scripts/
#
# 2005-10-21 initial version for Dovecot 1.0.
#
dir="$1"
if [ -z "$dir" ] || [ "$dir" = "-?" ] || [ "$dir" = "-h" ] || [ "$dir" = "--help" ]; then
  echo "Usage: $0 maildirpath"
  exit 1
fi
if [ ! -d "$dir" ] || [ ! -e "$dir/courierimapsubscribed" ]; then
  echo "$dir is not a path to a Courier maildir"
  exit 1
fi
find $dir -name courierimapsubscribed -print0 | xargs -0r rename -v 's/courierimapsubscribed/subscriptions/'
find $dir -name subscriptions -print0 | xargs -0r sed -i 's/INBOX\.//'
find $dir -name courierimapuiddb -print0 | xargs -0r rename -v 's/courierimapuiddb/dovecot-uidlist/'
find $dir -name courierimaphieracl -print0 | xargs -0r rm -vrf
find $dir -name courierimapacl -print0 | xargs -0r rm -vf
find $dir -name courierimapkeywords -print0 | xargs -0r rm -vrf

Comment to the script:
Hey Arto & everyone using this script:

Be careful when trying to run this on Red Hat Enterprise Linux or CentOS 4 systems. These operating systems ship with a different rename command than the Debian systems. You can also tell them apart based on the output when running ‘rename’ with no arguments.

This is the perl version which works:
Usage: rename [-v] [-n] [-f] perlexpr [filenames]

This is the RHEL/CentOS version that doesn’t:
call: rename.orig from to files…

Hope this helps someone out there, and thanks for the script Arto!

Source: http://bendiken.net/2005/11/03/courier-imap-to-dovecot-migration-script