[Dovecot] dspam plugin and updating of headers?

[Dan Swartzendruber]

Forgive me if this is a stupid question.  I know that when I drag a 
message to the SPAM folder, it is being trained properly, since the 
stats indicate so.  Dragging back to the inbox retrains it as ham.  I 
happened to notice that despite the fact that dspam says this in the 
debug log:

"appending header X-DSPAM-Reclassified: Spam"

nothing is actually being done to the message.  Looking at the debug log 
for a newly delivered message, I can see it is calling dovecot's deliver 
agent.  I am guessing here that this is just the way it works?  e.g. the 
plugin detects a message being moved from inbox to inbox.spam and calls 
dspam with the requisite arguments to retrain the message, but the 
message isn't really being modified?