Howto migrate mails from courier-imap without the passwords

August 26, 2013

I needed to move to a new mail server as the old one got too old. I had one problem – i didn’t know the old passwords of the virtual courier-imap users and the new system didn’t use the same hashing. It was ok to use new passwords for the new server, but as I needed to sync the most mails before I disabled the old mail server. This was needed as some users had really big mailboxes which would take too long to sync. So I needed a way to access the mails without knowing or reseting the old password. This post describes how I did the migration:

  1. I created a new user called “migrate” on the old mail server. I removed than its mail directory, in my case: rm -rf /var/mail/domains/penz.name/migrate
    And than I created a symlink to the mail of a user I wanted the mails to migrate:
    ln -s /var/mail/domains/penz.name/robert/ /var/mail/domains/penz.name/migrate
    Now I was able to login to the account with the “migrate” user and password
  2. For the migration I used the defacto standard “imapsync”. I called it for the first user to check if it worked correctly. (checked also the mails on the new server and so on …)
  3. Now I wrote a small script which did create a symlink, started imapsync, removed the symlink, create a new symlink, …… sure with some error handling 😉
  4. All of the above was done without the user noticing. Most Mails where now migrated except the changes to the old mailboxes after imapsync did its job.
  5. I did send a mail to the users telling them of the move to the new server and providing them with the exact date of the change and their new login data, and that it could take some hours until all of there mails were migrated.
  6. At the given date I changed the DNS entries to the new server and stopped the SMTP/Webmail service on the old server and made sure the IMAP service was only reachable for the imapsync script (with iptables – localhost and uid check). The users which already got to the new mailserver (be it with Webmail or IMAP) got most of their mails –  they others couldn’t connect until there dns server got the change. (It was done on a weekend)
  7. New mails from other SMTP servers where deferred or already delivered to the new server.
  8. After I made sure that the old mailboxes can’t be changed I started the script again and sync the differences to the server. This was now really fast as imapsync needed only to transfer a few mails.
  9. After the script was through I could switch the old server off.

I hope these steps help others  – if you’ve an other/better way to migrate, tell me about it in the comments. Thx.

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