Zammad can’t communicate with external systems

We installed Zammad on an UCS master. It start properly, but it can’t connect to external systems. It can neither connect to the UCS LDAP server (on the same machine), nor to an external mailserver. The error message is:

An error occurred: Can't connect to '' on port '7389', getaddrinfo: Temporary failure in name resolution

For the mailserver it’s also getaddrinfo: Temporary failure in name resolution.

It is mentioned here that this may happen, but for us a restart of the app does not help.

No idea if this is the correct way to check it on the command line, but it also fails:

root@univention:~# docker exec zammad_zammad-railsserver_1 ping
ping: Temporary failure in name resolution

as it’s the same machine you can maybe connect it directly using dockers IP:
ifconfig docker0
ifconfig docker1, 2 etc.

Hello @Andreas_T,

please open a topic in the Zammad Forum, where you can reach the app provider. Thank you very much.

Best regards,

We had two problems with our UCS / Zammad installation:

  1. We chose a zone that is managed by another nameserver, disabled the nameserver on the UCS machine and deleted the zone (this UCS master is only for Apps and user management). The name resolution worked again after re-adding the zone and starting the nameserver.

  2. Since Zammad is a multi-container App, it uses docker-compose and creates a new bridge for its networking. For some reason the bridge did not masquerade the source IP, so packets were only sent, but the recipient didn’t know the right IP address for replying. The following command fixes this until the next reboot:
    iptables -t nat -A POSTROUTING -s ! -o br-dc172dbdd5ba -j SNAT --to-source
    I think this is also fixed now via