Now that I received an answer, I explain my configuration.
exim current configuration:
#spamd_address = 172.17.2.230 783
spamd_address = 168.181.185.235 11333 variant=rspamd
warn message = X-Spam-Score: $spam_score
condition = ${if <{$message_size}{512k}{1}{0}}
spam = nobody:true/defer_ok
warn message = X-Spam-Score-Int: $spam_score_int
condition = ${if <{$message_size}{512k}{1}{0}}
spam = nobody:true/defer_ok
warn message = X-Spam-Bar: $spam_bar
condition = ${if <{$message_size}{512k}{1}{0}}
spam = nobody:true/defer_ok
warn message = X-Spam-Report: $spam_report
condition = ${if <{$message_size}{512k}{1}{0}}
spam = nobody:true/defer_ok
In Rspamd
cat milter_headers.conf
extended_spam_headers = true;
authenticated_headers = ["authentication-results"];
the rspamd documentation indicates that you just have to add the variable: extended_spam_headers = true
