Migration from Gmail to Dovecot
===============================

You can use <dsync migration via IMAP> [Migration.Dsync.txt] protocol, but
there are a few things different with Gmail compared to other IMAP servers:

 * With Gmail when you delete a mail from POP3, the mail is only hidden from
   future POP3 sessions, but it's still available via IMAP. If you wish to
   preserve this functionality, there's a 'pop3_deleted_flag' setting in
   Dovecot v2.2.2+.
 * Gmail has labels. If a message has multiple labels, it shows up in multiple
   IMAP folders, but it's still the same message and uses quota only once for
   that message. Dovecot currently doesn't have such support, so the migration
   will copy the message to multiple folders and each instance will use up
   quota. There's currently no easy fix for this, although there are some
   future plans to optionally not count message copies towards quota.
    * Even though the quota is duplicated, it doesn't mean that the storage
      usage has to be duplicated. Use the dsync -v parameter to avoid this. See
      https://github.com/dovecot/core/commit/70df8f39fb3db7c49b18c855178f8172176a037a
 * Gmail has virtual folders: "All Mail", "Starred" and "Important". From
   migration point of view this means that the migration should skip most of
   these folders, since their mails are in other folders anyway. With v2.2.3+
   you can tell dsync to skip these folders:'doveadm sync -x '\Flagged' -x
   '\Important'' - by using the \flag parameters dsync finds the folders by
   their SPECIAL-USE flag rather than their name (which may be different for
   different user depending on their language).
    * The "All Mail" folder actually contains also "archived mails" that don't
      exist in any other folder. These mails need to be migrated. See below.
 * Google requires that SSL/TLS be enabled to connect through IMAP. Make sure
   that the following are enabled in your Dovecot configuration and set to
   appropriate values based on your distribution (usually either one is
   enough):

   ---%<----------------------------------------------------------------------
     ssl_client_ca_dir = (''your distribution's trusted TLS CA store (Fedora /
   CentOS / Redhat uses /etc/pki/tls/ ))''
     ssl_client_ca_file = (''your distribution's trusted TLS CA file (Fedora /
   CentOS / Redhat uses /etc/pki/tls/cert.pem ))''
   ---%<----------------------------------------------------------------------

GMail Migration Feature (v2.2.16+)
----------------------------------

There's a new 'imapc_features=gmail-migration' setting that helps with this
migration. It will:

 * Set the pop3_deleted_flag to mails that no longer exist in POP3
 * Return POP3 UIDL in GMail format so dsync can preserve it.
 * Add a new $GmailHaveLabels keyword to archived mails in the \All mailbox,
   which means those mails are not archived. You probably don't want to migrate
   these mails.
    * Note that mails in the \Important and \Flagged mailboxes are marked with
      "\Important" and "\Starred" labels. If you don't migrate mails that have
      $GmailHaveLabels then you must not exclude the \Flagged and \Important
      mailboxes or some of the mails won't be migrated.

For example use a command line:

v2.2.16:

---%<-------------------------------------------------------------------------
doveadm backup -a 'virtual/All' -F '-$GmailHaveLabels' -R -u user@domain imapc:
---%<-------------------------------------------------------------------------

Unfortunately -F parameter isn't working in v2.2.17 & v2.2.18 because of
another parameter collision caused -F to be accidentally used for another
purpose. For v2.2.19+ use:

---%<-------------------------------------------------------------------------
doveadm backup -a 'virtual/All' -O '-$GmailHaveLabels' -R -u user@domain imapc:
---%<-------------------------------------------------------------------------

(This file was created from the wiki on 2019-06-19 12:42)