I am currently installing rspamd 1.7.9 on a Debian 9 server. Everything is working except the mx_check module. It always results in MX_INVALID. I already tried increasing the timeout, but I don't think it is a timeout issue. Enabling debug for the module does not produce any additional log messages. Enabling the debug logging for rspamd also does not create any additional information regarding that module. I know the module is enabled, as whitelisted domains are properly excluded from the mx check.
Does anyone know what the problem could be or how I could debug it? I ran out of ideas where to look.
Update 1:
I tried now with unbound, bind9 and no local DNS. Same result, so I don't think it is DNS related. Especially since DNS works for all the other modules