dovecot - Apr 2014 - dsync deleted my mailbox - what did I do wrong?

Hi.

Mostly annoying: I migrated from one machine to another, made sure the 
target host worked as expected, updated mx records and - after a couple of 
days - signed it off as good. This is just my private machine, no big deal 
if something goes wrong..

Everything's fine? Good, let's migrate my inbox from the old machine. 
There's no direct connectivity between those servers, so what I did was:

(old server)
sudo -u vmail dsync -u dar at darklajid.de backup maildir:/tmp/mail_backup/

Works fine, got my maildir. Tar'd it up, moved it to the new server. Now 
how do I import those mails? Ah, let's use the same command, with -R?

(new server)
sudo -u vmail dsync -u dar at darklajid.de -R backup maildir:/tmp/mail_backup
Error: Mailbox INBOX sync: mailbox_delete failed: INBOX can't be deleted.

Wait. What? Sure enough, the last couple of days are gone, the target 
mailbox is completely empty. I read the man page over and over again, but 
failed to see the problem. I even thought for a moment that _maybe_ dsync 
backup is one-way only (even if that failed as well) and tried the same 
command with mirror. Exactly the same output, same result, empty target 
mailbox.

In the end I succeeded to import the mails with doveadm import, completely 
lost a number of days of mails. My fault, sloppy not to back the up again, 
but I still don't think that this should happen. Ever.

My question now is:

- where did I fail (ignoring the backups, please. That's .. something I 
know)

- Can I use dsync ... for backups? I don't think that this is a good idea 
after yesterday night?

- Should dsync EVER try to delete mailboxes? Even 'special' mailboxes? 
Should it warn about that, asking for a --force switch or something?

Any insights would be appreciated. At this point the damage is done, but 
I'd like to learn how to do better.

Ben

Hi
>
> - where did I fail (ignoring the backups, please. That's .. something I
> know)
 From the man page: "backup - Backup mails from default mail location to 
location2 (or vice versa, if -R parameter is given). No changes are ever 
done to the source location. Any changes done in destination are
discarded."

The last sentence describes what happened to you: all new mail on the 
new machine is a "change" and was discarded (by deleting new mail.) If
I'm not mistaken, this is correct behaviour for backup mode - you get 
exact copy of the source side (maildir:/tmp/mail_backup) on destination 
side (dar at darklajid.de)
>
> - Can I use dsync ... for backups? I don't think that this is a good
> idea after yesterday night?
AFAIK you can safely use it to make the backup. I'm not sure if it can 
be reliably used to restore data (don't think so but I'm not an expert.)
I'd use doveadm import for that.