30 hops max

in conf.d/main/02_exim4-config_options:

  # rfc1413_hosts = *
- #rfc1413_query_timeout = 5s
+ rfc1413_query_timeout = 0s

disabling ident lookups makes sense because noone is operating a working ident server and it causes an unnecessary 5 seconds delay on clients that drop packages on their firewalls.