How to configure the Exim system filter in conjunction with Spamassassin?

Question

Exim

Good afternoon, the Exim SMTP server is running in conjunction with the Spamassassin (SA) anti-spam, which is running as a daemon. There is a task to change the heading of letters if SA has found out that the letter is spam. Decided to do through the system filter in Exim'e
configure

...
spamd_address = 127.0.0.1 783
system_filter = /usr/local/etc/exim/sa_exim
...

sa_exim

logfile /var/log/exim/mainlog

if "$message_headers" contain "X-Spam-Flag: Yes"
    then
        headers add "Old-Subject: $h_subject:"
        headers remove "Subject"
        headers add "Subject: (*F* SPAM *F*) $h_old-subject:"
        logwrite "---Marking as spam---"
endif

SA successfully processes letters and gives them points, but the system filter does not work. I understand that SA does not put a flag on letters that are marked as spam. What condition should I put in the if in the filter so that Exim can successfully change the headers of spam emails without touching the regular ones?

Answer 1

If I'm not mistaken then X-Spam-Flag: 1, not Yes. But I could be wrong, there is no way to look at their servers right now.

Answer 2

I understand that SA cannot modify the messages in this bundle itself, so it simply checks and reports that the letter is / is not spam to Exim, which in turn, based on this information, must modify the letter as we need. But I don't understand what condition to put in the system filter so that Exim understands that this message is spam.