That's not how it works. I can assure you my logs have "SA dbg:” lines only for
messages which recipient address matches the @debug_recipient_maps.
It triggers a DEBUG_ONESHOT event in Amavisd-new, and when the message is fully
processed in spamassassin, Amavisd-new turns of DEBUG_ONESHOT:
Jun 27 15:31:22 my.mx.server amavis[240694]: (240694-15) DEBUG_ONESHOT:
TURNED ON
../..
Jun 27 15:31:24 my.mx.server amavis[240694]: (240694-15) DEBUG_ONESHOT:
TURNED OFF
This kind of DEBUG_ONESHOT yields to ~ 1900 lines of log, instead of just one
or two lines when recipient address does not match @debug_recipient_maps. I
would have noticed.
Then you must have "$log_level = 0" and your setup already experiences
what I have described.