combrk Can I define which external DNS server to use for the DNS check?
If we look here you can see the defaults.
Now if you use grommunio-admin config dump
you might see the following in there
dns:
dudIP: 172.16.254.254
externalResolvers:
- 1.1.1.1
- 1.0.0.1
you can copy that into e.g. /etc/grommunio-admin-api/conf.d/dns.yaml
and change it to your needs.
After that i would either restart the service systemctl restart grommunio-admin-api.service
or if in doubt the whole system.
This is untested but i think that should do.