I found the wiki on installing Zimbra on gentoo (debian chroot) very useful for my needs, however there is one point in the whole document that is missing:
The configuration for mail queues. I did found a way to get it to work, and here's how to (maybe you could include this in the wiki?)

  1. chroot into zimbra
    chroot /zimbra
  2. install ssh
    apt-get install ssh
  3. edit /etc/sshd_config and set the port to 23 (in order not to collide with gentoo's sshd)
    port 23
  4. start sshd
    /etc/init.d/ssh start
  5. su into zimbra
    su - zimbra
  6. change zimbra's ssh port to 23 (or another one)
    zmprov ms MAIL.DOMAIN.COM zimbraRemoteManagementPort 23
    substitute MAIL.DOMAIN.COM with the fqdn of your host name and make sure the port is set to the one you set in your /etc/sshd_config file!
  7. generate new ssh keys
  8. deploy the keys

to test this, you can run the following command
ssh -i .ssh/zimbra_identity -o strictHostKeyChecking=no zimbra@MAIL.DOMAIN.COM -p 23
again, substitute MAIL.DOMAIN.COM with the fqdn of your host name, and change the port (-p 23) to the one you set your machine on
You should not get any password prompt.

Hope this is of any help for anyone.