This documentation is for Dovecot v1.x, see wiki2 for v2.x documentation.
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Migration to Dovecot

WARNING: Badly done migration will cause your IMAP and/or POP3 clients to re-download all mails. Read this page carefully.

This page contains generic information related to migrating from another IMAP or POP3 server to Dovecot. You should read this page, and then look at the server-specific instructions:

Dovecot is one of the easiest IMAP servers to migrate to because of its powerful configuration options. Dovecot can store email in both mbox and Maildir formats, making it compatible with many existing servers. Dovecot is also very flexible as to where it stores the email. It supports many different databases for storing passwords user information.

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 it is likely to read your existing mailboxes and user and password configurations. Tasks for conversion include:

IMAP migration

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

  1. Message flags
    • Lost flags can be really annoying, you most likely want to avoid it.
  2. Message UIDs and UIDVALIDITY value
    • If UIDs are lost, at the minimum clients' message cache gets cleaned and messages are re-downloaded as new.
    • Some IMAP clients store metadata by assigning it to specific UID, if UIDs are changed these will be lost.
  3. Mailbox subscription list
    • Users would be able to manually subscribe them again if you don't want to mess with it.

POP3 migration

When migrating mails from another POP3 server, you should try to preserve the old UIDLs. If POP3 client is configured to keep mails in the server and the messages' UIDLs change, all the messages are downloaded again as new messages.

Don't trust the migration scripts or anything you see in this wiki. Verify manually that the UIDLs are correct before exposing real clients to Dovecot. You can do this by logging in using your old POP3 server, issuing UIDL command and saving the output. Then log in using Dovecot and save its UIDL output as well. Use e.g. diff command to verify that the lists are identical. Note that:

  • If a client already saw changed UIDLs and decided to start re-downloading mails, it's unlikely there is anything you can do to stop it. Even going back to your old server is unlikely to help at that point.

  • Some (many?) POP3 clients also require that the message ordering is preserved.
  • Some clients re-download all mails if you change the hostname in the client configuration. Be aware of this when testing.

Some servers (UW, Cyrus) implementing both IMAP and POP3 protocols use the IMAP UID and UIDVALIDITY values for generating the POP3 UIDL values. To preserve the POP3 UIDL from such servers you'll need to preserve the IMAP UIDs and set pop3_uidl_format properly.

If the server doesn't use IMAP UIDs for the POP3 UIDL, you'll need to figure out another way to do it. One way is to put the UIDL value into X-UIDL: header in the mails and set pop3_reuse_xuidl=yes. Some POP3 servers (QPopper) write the X-UIDL: header themselves, making the migration easy.

Some POP3 servers using Maildir uses the maildir base filename as the UIDL. You can use pop3_uidl_format = %f to do this.

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

  • UW-POP3: pop3_uidl_format = %08Xv%08Xu

  • qmail-pop3d: pop3_uidl_format = %f

  • Cyrus <= 2.1.3: pop3_uidl_format = %u

  • Cyrus >= 2.1.4: pop3_uidl_format = %v.%u

  • Citadel (all versions): pop3_uidl_format = %u

  • Dovecot 0.99: pop3_uidl_format = %v.%u

  • tpop3d:

    • Maildir: pop3_uidl_format = %Mf (MD5 sum of the maildir base filename in hex)

    • mbox: MD5 sum in hex of first 512 bytes of the message (or of the full message if it's less than 512 bytes).
  • popa3d Generates MD5 sum from a couple of headers. Dovecot uses compatible MD5 sums internally, but converts them into UIDL strings in a bit different way.

  • teapop 0.3.8:

    • Maildir: pop3_uidl_format = %Mf (MD5 sum of the maildir base filename in hex)

    • mbox: MD5 sum of the message without the following lines: Status,X-Status,Lines and Content-Length.
  • Cucipop mbox: v1.31 uses its own homebrew checksum based on headers and body. Injection of X-UIDL: headers and pop3_reuse_xuidl=yes is the way to go.
  • qpopper: pop3_reuse_xuidl=yes

IMAP <-> IMAP copying

If you don't care about preserving messages' UIDs, or if there isn't a simple way to preserve them, you can always migrate from another IMAP server to Dovecot by downloading the messages via IMAP from the old server and then uploading them to Dovecot via IMAP.

There are several different tools for this, for example UW-IMAP's mailutil, imapsync and YippieMove.


Here's an example of how to run imapsync for a single user:

imapsync --syncinternaldates \
  --host1 --authmech1 LOGIN --user1 --password1 secret \
  --host2    --authmech2 LOGIN --user2 --password2 secret

It is quite easy to script this for a number of users, assuming you have their passwords. Even if you do not, imapsync also supports logging in as an admin user that has the ability to copy message for sub users, and a variety of other authentication options.

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