This documentation is for Dovecot v1.x, see wiki2 for v2.x documentation.
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See also the [http://bendiken.net/scripts/ courier2dovecot] script by Arto Bendiken.

TableOfContents

Migration to Dovecot

Dovecot is one of the easiest IMAP servers to migrate to because of its very powerful configuration options. Dovecot can store email in both MBOX and MAILDIR formats making it compatible with most other mail storage formats. It is very flexible as to where it stores the email. Dovecot supports many methods for storing user data and password authentication. You can set it up to authenticate against multiple databases.

Migration involves several separate tasks. You either need to convert your data or make Dovecot read your existing data. Dovecot is very good at being compatible and configurable so that it is likely to read your existing mail folders and user and password configurations. Tasks for conversion include:

  • Where and how to store the email
  • User configuration - home directory structure - UID/GID - password storage
  • Authentication of users

When migrating from one IMAP server to another, you should make sure that these are preserved:

  • Mailbox subscription list
    • User would be able to manually subscribe them again if you don't want to mess with it.
  • Message UIDs
    • If UIDs are lost, at the minimum clients' message cache gets cleaned
    • Some IMAP clients store metadata by assigning it to specific UID, if UIDs are changed these will be lost.
  • Message flags
    • Lost flags can be really annoying, you most likely want to avoid it.

Here's the more server-specific instructions:

UW-IMAP

By default UW-IMAP allows access to whole home directory, and many people have chosen to store their mails in mail/ directory. This usually means that IMAP clients have set "IMAP namespace" to "mail/", which doesn't work well with Dovecot, as Dovecot by default uses mail/ directory directly. So if IMAP namespace is kept as "mail/", Dovecot would try to access "~/mail/mail/" directory.

So, removing the prefix from IMAP clients would be the first step. Next problem is that subscribed mailboxes are listed as "mail/box" or "~/mail/box" or "~user/mail/box" in subscriptions file. You'd have to remove the mail/ directory part from all of these. The subscriptions file name is also different, UW-IMAP uses .mailboxlist while Dovecot uses .subscriptions.

Dovecot uses UW-IMAP compatible UID and message flag headers in mboxes, so that's not a problem.

Settings:

default_mail_env = mbox:~/mail:INBOX=/var/mail/%u
# make sure mbox_locks are the same with all software that accesses your mboxes
mbox_locks = dotlock fcntl

If you want to make a transparent migration to Dovecot without having to change the configuration on hundreds of client systems, you will need a slightly different configuration.

  • If your clients have the server prefix set to something like "~/mail", this will not work unless you enable mail_full_filesystem_access in your Dovecot configuration. Dovecot will otherwise reject mailbox names or prefixes that start with "~". Alternative to this with 1.0-tests is to [wiki:Namespaces set up multiple hidden namespaces].
  • You can either rename your ".mailboxlist" file to ".subscriptions" for all you users, or change the definition of SUBSCRIPTION_FILE_NAME in src/lib-storage/subscription-file/subscription-file.c. In 1.0-test, this value is defined in src/lib-storage/subscription-fileindex/maildir/maildir-storage.h and src/lib-storage/subscription-fileindex/mbox/maildir-storage.h.

  • If ~/mbox file exists, UW-IMAP moves mails from /var/mail/user there. Currently Dovecot doesn't support this feature, so you'll have to either move everyone's mails to ~/mbox and reconfigure MTA/LDA to store mails there, or alternatively get the ~/mbox users to move their mails back to /var/mail/user. This feature may be implemented later, but it's not planned in near future.
  • You should read [http://people.redhat.com/rkeech/maildir-migration.txt]. This document describes the migration process using scripts if you want to migrate from UW_IMAP with mbox to Dovecot using maildir (which will increase performance).

--- DON'T DELETE THIS MESSAGE -- FOLDER INTERNAL DATA ---

Only concerns Dovecot 0.99.x versions, 1.0-releases use them:

Every folder on a system using UW-IMAP has a system message in the top with the subject "DON'T DELETE THIS MESSAGE -- FOLDER INTERNAL DATA". This system message has information about the folder and its state. Dovecot 0.99.x does not use these system messages to anything so you can delete them without any problems - unless you have users using Pine together with an IMAP or POP3 mailclient.

UW-POP3

By default Dovecot generates POP3 UIDs differently than UW-IMAP. If you want to preserve them, with 0.99.x you'll have to [http://dovecot.org/patches/pop3-uidl-uwimap.patch patch Dovecot]. With 1.0-tests you can use:

pop3_uidl_format = %08Xv%08Xu

VIMAP

VIMAP or [http://vimap.sourceforge.net/ Virtual Imap] was a patched version of WU-IMAP that was modified to work with [http://www.solucorp.qc.ca/linuxconf/ Linuxconf's] virtual email configuration. The project doesn't seem to have much life and [mailto:patrik.hall@multitronic.fi Patrick Hall] who wrote the patch is thrilled that Dovecot can now be configured to be fully compatible. Details of how to do this are described in the [wiki:VirtualUsers Virtual Users] section.

Converting from MBX to MBOX

If you are using WU-IMAP and using the MBX format you will need to convert it to MBOX format. The conversion process isn't pretty, but here's a script that works. You will need to get and compile the mailutil program from the WU-IMAP web site.

# Written by Marc Perkel - public domain
# Usage mbx-convert <filename>
# This code assumes a user named "marc". Change to any real user on your system.
# Yes - it look bizzare - but it gets the job done

# First copy to users home dir and make the user the owner
cp "$*" /home/marc/in
chown marc:marc /home/marc/in

# Run mailutil to convert as the user other than root 
# mailutil requires this
su - marc -c "/usr/bin/mailutil copy in \#driver.mbx/out"

# cat instead of copy preserves the original owner and permissions
cat /home/marc/out > "$*"

# cleanup
rm /home/marc/in
rm /home/marc/out

Make a copy of some folders and test it first. Once you are satisfied that it works then:

  • Write a script to convert all your files.
  • Shut down your email system so files can't be modified
  • Copy all your email to a backup location in case you have to revert
  • Run the script
  • Turn on Dovecot and test to verify it is working
  • Important - make sure that you changed your SMTP configuration to write MBOX and not MBX.
  • Turn on SMTP and verify it is all working

Courier

Courier by default uses "INBOX." as private IMAP namespace, so it has exactly the same problems as described with UW-IMAP above. Again, if you want the migration to be transparent for IMAP clients see [wiki:Namespaces Namespaces] how to get namespaces to be Courier-compatible.

  • Courier's courierimapsubscribed is compatible with Dovecot's subscriptions file, just rename it and remove the "INBOX." prefixes. (NOTE: with 0.99.x it's .subscriptions', with 1.0 it's subscriptions' without the dot)

  • Courier's courierimapuiddb is compatible with Dovecot's dovecot-uidlist file, just rename it.

  • Courier's message flags are compatible with Dovecot (as it's specified by Maildir specification)
  • Courier's message keywords implementation isn't Dovecot compatible and there's currently no easy way to migrate them.

See also the [http://bendiken.net/scripts/ courier2dovecot] script by Arto Bendiken.

Settings:

# normal home directories
default_mail_env = maildir:~/Maildir
# for virtual users
default_mail_env = maildir:~/

For POP3 UIDL compatibility, use one of:

# Courier version 0 (using maildir filenames)
pop3_uidl_format = %f
# Courier version 1 (UID)
pop3_uidl_format = %u
# Courier version 2  (UIDVALIDITY and UID)
pop3_uidl_format = %v-%u

Cyrus

See [http://madness.at/projects/ cyrus2courier], it's Dovecot-compatible. Also mirrored at [http://dovecot.org/tools/ dovecot.org].

For POP3 UIDL compatibility, use one of:

#  Cyrus (old format - up to v2.1.3)
pop3_uidl_format = %u
#  Cyrus (new format - v2.1.4 and above)
pop3_uidl_format = %v.%u

Other POP3 servers

Some POP3 servers generate the X-UIDL header. To use this header when available and ease migration, use:

# Use X-UIDL header if available
pop3_reuse_xuidl = yes

Different POP3 servers generate UIDs differently. If you want to preserve them to avoid users downloading their mails twice, you'll need to figure out how the server generates the UID and patch Dovecot accordingly to do the same.

Here is a list of POP3 servers and how they generate their UIDs. Please update if you know more:

  • [http://www.openwall.com/popa3d/ popa3d] Generates MD5 sum from a couple of headers. Dovecot uses compatible MD5 sums internally but converts them into strings in a bit different way.

None: Migration (last edited 2010-11-02 22:24:58 by TimoSirainen)