I like getting mail with the subject modified with a message to say it is spam, but in looking up how to configure exim to since by default it wasn't, I found how to get a little more out of it.
Now instead of my spam folder being filled with subjects that start with ***SPAM***, they now start with **SPAM (score)** so I can see easily which ones tripped the most (anything over 10, I just delete), and anything under 10, I'll give a glance to see if the sender/subject may be legit.
Service Configuration -> Exim Service Configuration
Choose the "Filters" tab
If the first option (System Filter File) is set to "None", use the default value.
I can't recall if my base install was "None" or Set to the default value, but either case, that default file didn't exist until things were changed on my install, but regardless, out of the gate, the other "default" values were not being applied.
For the bottom option, the prefix for Subject, it defaults to ***SPAM***
This is a good start, but in looking around (because I didn't realize this default file didn't exist and at first I manually created it), I found that if you change the value to be **SPAM ($spam_score)** It will then add the Spam Score into the subject line.
Example sitting in my Spam Folder now: **SPAM (17.2)** An old friend has searched for you. Contact them
Now in my e-mail app, After all specific filters, I have it say any subject starting with **SPAM ( goes into a spam folder
Works pretty nifty.
If you want to test it, send yourself an e-mail with the following line in it:
Ok, for those who may mention it, there is a (?) help link on that item, and right in there it even gives an example of using the $spam_score... I didn't know that was there, as like I mentioned, on my system since the config file didn't exist, the default listed ***SPAM*** didn't even work so I went digging to do it manually.