Previous aarrangement was ISPCONFIG ->Unifi DMP -ISP's router-> ONT fibre. Removed ISP router and connected unifi DMP directly to ONT fibre. Since then a small proportion of legitimate emails (e.g. proton mail) arriving to ISPConfig server are getting blocked. "Diagnostic-Code: smtp; 554 5.7.1 Service unavailable; Client host [109.224.244.17] blocked using zen.spamhaus.org; Error: open resolver; https://check.spamhaus.org/returnc/pub/172.68.0.87/" Nothing has changed on ISPconfig server. Any thoughts on why they are now getting blocked? Gemini suggests 'to use a dedicated, local caching DNS resolver (e.g., Unbound or a local BIND instance) for all DNS lookups, especially for DNSBLs.' As I understand it, currently, all DNS for the domains on the ISPConfig server are managed by AWS Route53. I welcome suggestions to resolve(!) the issue.
There are several threads because of this issue. See here: https://forum.howtoforge.com/thread...-issue-credit-to-nhybgtvfr.94238/#post-466022
I recommend to remove the RBL under System > server config > mail. New ISPConfig install do not use it anymore anyway.
