Moving mailboxes from Courier/Maildir to DirectAdmin/dovecot/Maildir

I have an old mail server running Postfix and courier-imap. We want to split our customers off onto their old server, preferably something with a pretty pointy-clicky interface so that they can manage their own accounts. (Yes, people do still buy email service these days.)

The old server runs FreeBSD, postfix, and courier-imap. The new server runs FreeBSD 9.2 with DirectAdmin. DirectAdmin is a canned package that puts a customer-friendly front end on a whole bunch of standard Unix software. (Why FreeBSD? ZFS. When my customers fill up the hard disk, I can just “zfs send” the whole machine to bigger disk.)

The good news is, both my old server and the new one use Maildir. The bad news is, they’re arranged slightly differently and have somewhat different file formats. Tools exist to do 80% of the migration for you, but my setup has a few edges.

I suspect that nobody else has my exact legacy setup, and my readers don’t care about this level of detail. I also suspect that the migration project will last weeks and I will completely forget how I did it in between individual customer migrations, so I’m writing this anyway. But maybe someone else can learn something from it, even if it’s just “man, I would never hire this Lucas character.”

Create your email domain and all the user accounts in DirectAdmin. I don’t know any way to migrate encrypted virtual user passwords from Postfix into DirectAdmin, so I’ll need to create new passwords for the users. That’s not uncommon for a packaged mail server migration, so my users will live with it. This is a tedious point-and-click operation, but point-and-click is the point of DirectAdmin, so give the job to a minion and get it done.

But how to transparently migrate the mailboxes from the Courier server to Dovecot?

On the old server, the mailboxes are in /disk2/mail/vhosts/domainname/account/. On DirectAdmin, the mailboxes are in /home/userid/imap/domain/account/Maildir/. I can tar up the old accounts and drag the whole directory over to the new server, but I need to massage the directories so that they’re arranged properly.

Courier and Dovecot both use files to store mailbox state information. IMAP state is important. Without it, users will re-download every single message. I don’t care about the bandwidth or the disk I/O this will cause, but the users will complain. Complaints lead to meetings, and meetings lead to the Dark Side. There’s a script to convert from one to the other. Dovecot also has good migration documentation, I recommend you read that before doing your own migration.

The file ownership needs correcting. DirectAdmin creates user accounts for each customer (more or less), and that account needs to own the email files for the various domains.

So, what am I willing to do manually?

I will manually tar up the domain’s mail directory, copy it to the destination server, and untar it in /home/userid/imap/domain/. And I’m willing to provide the username that should own the files. I’m sure both of these could be automated, but I don’t have enough accounts to migrate to do this correctly.

I’m not willing to move files around or run migration scripts. Because these are things that human beings mess up.

There’s ways to do this in shell scripts, but I’m using Perl. Because while my Perl makes small children cry, my shell scripts feature in rituals praising Nyarlathotep.

So, the script:

#migrate from old mail server to new
#run from domain directory
#Takes one argument, the username expected to own the files when done.

unless ($ARGV[0]) {
die "\nNeed a username to own files!\n\n";

opendir (USERS, ".") || die "Cannot open current directory";

foreach $user (readdir (USERS)) {

next if ($user =~ /^\.{1,2}$/);
print "Converting $user...\n";
mkdir ("$user/Maildir") || die "Cannot make Maildir";
opendir (USERDIR, "$user") || die "Cannot open user directory";
foreach $file (readdir (USERDIR)) {
next if ($file =~ /^\.{1,2}$|Maildir/);
print "Moving $user/$file\n";
rename ("$user/$file","$user/Maildir/$file")
|| die "Cannot move $file";
#next user
print "Now performing courier-dovecot migration...\n";
system (" --to-dovecot --recursive --convert");
print "Fixing ownership...\n";
system ("chown -R $ARGV[0]:mail .");

Is this pretty trivial? Yep. But the most error-prone part of any process is the part I do. The more of the migration the machine does, the fewer screw-ups in the migration.