This documentation is for Dovecot v2.x, see wiki1 for v1.x documentation.

Converting between mailbox formats

If you want a transparent migration, the biggest problem is preserving message UIDs. See Migration for the problems this may cause. If you do the conversion with dsync, it preserves the UIDs.


With dsync you can convert between any two mailbox formats that Dovecot supports. As much of the mailbox state is preserved as possible. Typically it's everything. See Tools/Dsync for full documentation, here are only a couple of examples:

If you can successfully use dsync, you can skip the rest of this page.

Converting from mbox to Maildir

Check also the User-Contributed Maildir Support section on the qmail community site for more choices.

Example (user's mail in ~someuser/mail and INBOX in /var/mail/someuser):

cd ~someuser -s mail -R -m -s /var/mail/someuser
mv mail mail.old

Now the mail will be in ~someuser/Maildir. Do not forget to migrate the subscriptions as well, otherwise the new maildir will seem to have only an inbox when viewed through a mail client that supports them. This can be as simple as copying the old ~someuser/mail/.subscriptions file to ~someuser/Maildir/subscriptions (warning: I have not tested this extensively, my subscription list and folder hierarchy was very simplistic).

Hierarchy separator change

The default hierarchy separator with Maildir is '.' instead of '/' which is common with mboxes. To keep the migration transparent to users, you can keep the '/' separator by using namespaces. In any case you need to replace the '/' with '.' in the subscriptions file:

UW-IMAP's subscriptions file is in ~/.mailboxlist. Dovecot's mbox subscriptions is in <mbox root dir>/.subscriptions. Dovecot's Maildir subscriptions is in <maildir root>/subscriptions.

Also if you're migrating from UW-IMAP, you probably had "mail/" prefixes in the mailbox names. You can again use namespaces to let clients use the prefix, or you can tell your users to remove the namespace prefix from their clients and change the subscriptions file:

sed 's/^mail\.//' subscriptions >
mv subscriptions

Note that because Maildir uses '.' as the hierarchy separator in filesystem, it's not possible to have mailbox names containing '.' characters, even if you changed the separator in namespaces. If you really want to have dots, the only way to do this is by modifying the filesystem separator in MAILDIR_FS_SEP and MAILDIR_FS_SEP_S defines in src/lib-storage/index/maildir/maildir-storage.h file in the sources. Do not be tempted to change MAILDIR_FS_SEP et al to '/'; it won't work.

Converting from Maildir to mbox

This is especially helpful if you want to archive your mail to a single file for storage on a CD, a PC, etc. But it can also be helpful if you want to use mbox with Dovecot.

Use the reformail program that comes with maildrop. You can also use the formail program that comes with procmail. Here is a simple script showing how this works.

To use it, adjust the script to invoke the right command according to your system.

Then cd to the user's home directory (one level above Maildir) and run the script with two arguments: the mailbox name (You can use "." for the top-level folder), and the output mbox filename, for example:

cd ~hans
perl . >/tmp/hans-inbox
perl Sent >/tmp/hans-sent

#!/usr/bin/env perl
# dw = Dovecot Wiki :-)
# NOTE! The output file must not contain single quotes (')!
# figure out which program to run
$cmd="reformail -f1";
system("$cmd </dev/null >/dev/null 2>/dev/null") == 0 or $cmd="formail";
system("$cmd </dev/null >/dev/null 2>/dev/null") == 0
or die "cannot find reformail or formail on your \$PATH!\nAborting";
if (($outputfile eq '') || ($dir eq ''))
{ die "Usage: ./ mailbox outputfile\nAborting"; }
if (!stat("Maildir/$dir/cur") || !stat("Maildir/$dir/new"))
{ die "Maildir/$dir is not a maildir.\nAborting"; }
@files = (<Maildir/$dir/cur/*>,<Maildir/$dir/new/*>);
foreach $file (@files) {
  next unless -f $file; # skip non-regular files
  next unless -s $file; # skip empty files
  next unless -r $file; # skip unreadable files
  $file =~ s/'/'"'"'/;  # escape ' (single quote)
  $run = "cat '$file' | $cmd >>'$outputfile'";
  system($run) == 0 or warn "cannot run \"$run\".";

Converting from MBX to Maildir

See the as mentioned on the Migration/UW page.

Converting from MBX to mbox

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

#! /bin/sh
# Written by Marc Perkel - public domain
# overhauled by Matthias Andree, 2006
# Usage: mbx-convert <filename>
# This code assumes there a user named "marc" with the primary group "marc".
# Change to any real user on your system.
# Yes - it look bizzare - but it gets the job done
# abort on error
set -e
if [ $# -ne 1 ] ; then
  echo >&2 "Usage: $0 <filename>"
  exit 1
# set up automatic cleanup
trap 'rm -f "${homedir}"/in.$$ "${homedir}"/out.$$' 0
# First copy to users home dir and make the user the owner
cp "$1" "${homedir}/in.$$"
chown "$user":"$group" "${homedir}/in.$$"
# Run mailutil to convert as the user other than root
# mailutil requires this
su "$user" -c "mailutil copy in.$$ \#driver.unix/out.$$"
# create new file with same permissions/owner as old
cp -p "$1" "${1}.new"
# cat instead of copy leaves the original owner and permissions alone
if cat "${homedir}/out.$$" >"${1}.new" ; then
  # cat succeeded, rename file into place
  mv "${1}.new" "$1"
  # cat failed, remove temp file
  rm -f "${1}.new"
  exit 1

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

User comments:

None: Migration/MailFormat (last edited 2019-01-11 08:40:22 by AkiTuomi)