[Dovecot] Failing: doveadm sync <--remote host--> dsync mirror

[Michael Grimm]

Hi --

I'm used to dsync my two mailservers running 2.0.16. 


Today, I did upgrade one server to 2.1, and doveadm sync is throwing to following error:

mail> doveadm sync -f -u test ssh vmail at remote-host.tld dsync -v -f -u test
doveadm(test): Fatal: All your namespaces have a location setting. It should be empty (default mail_location) in the namespace to be converted.


Same error with old running command:

vmail> dsync -v -f -u test mirror ssh vmail at remote-host.tld dsync -v -f -u test
doveadm(test): Fatal: All your namespaces have a location setting. It should be empty (default mail_location) in the namespace to be converted.


Here's an excerpt of my doveconf -n:

mail> doveconf -n
mail_home = /var/mail/homedirs/%n
mail_location = mdbox:/var/mail/maildirs/%n
passdb {
  args = /usr/local/etc/dovecot/dovecot-sql.conf
  driver = sql
}
userdb {
  driver = prefetch
}
userdb {
  args = /usr/local/etc/dovecot/dovecot-sql.conf
  driver = sql
}


Reverted back for the time being (production servers) until I do understand the issue. 
Searching Google with "Fatal: All your namespaces have a location setting." only shows closed bugs back in 2010.

Do I have to upgrade both servers to get syncing running?
Any hint, help is highly appreciated.

Thanks, 
Michael