I’ve just migrated a couple of servers from Courier-IMAP to Dovecot, and am very happy with the latter so far. I thought I’d share the courier2dovecot shell script I whipped together (based on the instructions I found in the migration how-to), for converting Courier-IMAP maildirs to Dovecot format.

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