What is the recommended procedure to migrate from mbox to maildir on a server
already running dovecot? Ideally, this procedure would convert messages in an
existing mbox INBOX and in ~/mail mboxes (as defined in my dovecot
configuration) to storage in a ~/Maildir. Some of the INBOXs are rather large
-- 100's of MB (one of the reasons for migrating).
What I have tried has not worked for me. Below, I describe what I tried, how I
tested before I tried, what went wrong, and the current setup (pre-migration).
What I tried:
=============
stop exim4
service dovecot stop
Make dovecot listen only locally, not to external connections.
/etc/dovecot/local.conf
protocol imap {
listen = 127.0.0.1:143
ssl_listen = 127.0.0.1:993
}
protocol pop3 {
listen = 127.0.0.1:110
ssl_listen = 127.0.0.1:995
}
Modify dovecot configuration for maildir:
Watch capitalization!
#in 10-mail.conf:
mail_location = maildir:/home/%u/Maildir
namespace inbox {
separator = /
}
dovecot -n, to confirm results and perform
limited syntax checking.
service dovecot start
for each user, in a bash script:
dsync -v -u "$U" mirror "mbox:/home/$U/mail:INBOX=/var/mail/$U"
(if the conversion worked for all users, then reconfigure exim to use maildir
and restart it; reconfigure dovecot to listen to external interfaces and
restart.)
How I tested:
=============
Before trying this on the real server, I set up a matching (same versions of
Debian, Exim, and Dovecot) VM using mbox, with a couple of accounts. One using
POP3, one using IMAP. The IMAP account was accessed from Claws and from
Outlook. The test accounts had perhaps a dozen messages on the server. I
tried the conversion procedure, and everything I tried worked flawlessly.
(Yes, next time I will move some real inbox files from the live server).
What went wrong:
================
I encountered two types of problems here. The first was several dsync warnings
(username changed):
dsync(example): Warning: Mailbox changes caused a desync. You may want to run
dsync again: Remote lost mailbox GUID 21bfa11a81f11763ac150000d09efc50 (maybe
it was just deleted?)
As I understand it, this can result in some or all messages being downloaded
again by clients. My understanding may be wrong. I also don't understand how
the mailbox could have changed -- exim4 was stopped, dovecot is only listening
on 127.0.0.1, and I am the only user who uses a local mail client on that
system, and this was not my account.
The second problem I encountered seems to match Debian Bug report logs -
#1011238.
In part of the discussion of that report, the reporter mentions adding -1 to
the command, as shown:
dsync -v -u "$U" mirror -1 "mbox:/home/$U/mail:INBOX=/var/mail/$U"
While this seemed to eliminate the dsync panic of #1011238, as far as I can
tell, no old messages were actually moved from the old mbox files to the new
maildirs. At that point I restored the backup mbox files and undid the changes
to dovecot and exim4.
Current setup:
==============
Debian 11.4
Exim 4.94.2-7
dovecot 1:2.3.13+dfsg1-2
The current setup with Dovecot was a successful migration from IMAP-UW in
December 2020.
Output from dovecot -n
(the list of trusted networks has been removed)
# 2.3.13 (89f716dc2): /etc/dovecot/dovecot.conf
# Pigeonhole version 0.5.13 (cdd19fe3)
# OS: Linux 5.10.0-16-686-pae i686 Debian 11.4
# Hostname: localhost
auth_verbose = yes
mail_location = mbox:~/mail:INBOX=/var/mail/%u
mail_privileged_group = mail
namespace inbox {
inbox = yes
location =
mailbox Drafts {
special_use = \Drafts
}
mailbox Junk {
special_use = \Junk
}
mailbox Sent {
special_use = \Sent
}
mailbox "Sent Messages" {
special_use = \Sent
}
mailbox Trash {
special_use = \Trash
}
prefix =
}
passdb {
driver = pam
}
pop3_uidl_format = %08Xv%08Xu
protocols = " imap pop3"
ssl_cert = </etc/dovecot/dovecot.pem
ssl_client_ca_dir = /etc/ssl/certs
ssl_dh = # hidden, use -P to show it
ssl_key = # hidden, use -P to show it
userdb {
driver = passwd
}
Thank you to anyone who read this far.
Ken
