spam assassin URLBL lookup are blocked thus not working - this is why

[Alexander]

In email headers, in the X-Spam-Status, I get URIBL_BLOCKED which indicates that URLBL lookups are blocked

in etc/resolv.config, the value for nameserver is 8.8.8.8 which is the dns server from google.

URIBL provides public lookups over DNS for low volume usage. If you spam check a large amount of email, or you use a shared DNS platform for resolution, you may receive a response saying the query was refused. That said, Public DNS providers such as OpenDNS or Google Public DNS are effected due to the high volume of queries they generate, as are many other internet service providers (ISP) that use caching nameservers for their customer base.

See this for info: http://uribl.com/refused.shtml

Better practise would be to take the name server by the internet provider you are connected to or to give the opportunity to set it manually to the dns given by your provider.

is it possible to override this file with the _override option ?

[SH]

You don't need to override DNS settings unless you really want to. Docker is handling resolv.conf itself - you should see something like this from container:

/dev/mapper/ubuntu--vg-root on /etc/resolv.conf type ext4 (rw,relatime,errors=remount-ro,data=ordered)

Basicaly it takes settings from your host system, see https://docs.docker.com/engine/userguide/networking/default_network/configure-dns/

[SH]

So either you change host resolv.conf OR set dockerd daemon settings with --dns=IP_ADDRESS...

[Alexander]

Thanks for the hint - did so: After changing DNS to my provider's DNS, it's working.