Extract from /etc/spamassassin/local.cf
# Bayesian classifier auto-learning (default: 1)
# activated
bayes_auto_learn 1
### added lines start ###
bayes_auto_expire 0
bayes_journal_max_size 15000000
bayes_expiry_max_db_size 20000000
### added lines end ###
# Set headers which may provide inappropriate cues
# to the Bayesian classifier
#
# bayes_ignore_header X-Bogosity
# bayes_ignore_header X-Spam-Flag
# bayes_ignore_header X-Spam-Status
### added lines start ###
bayes_ignore_header Return-Path
bayes_ignore_header Received
bayes_ignore_header X-Spam-Flag
bayes_ignore_header X-Spam-Status
bayes_ignore_header X-Spam-Flag
bayes_ignore_header X-Spam-Level
bayes_ignore_header X-purgate
bayes_ignore_header X-purgate-ID
bayes_ignore_header X-purgate-Ad
bayes_ignore_header X-GMX-Antispam
bayes_ignore_header X-Resent-For
bayes_ignore_header X-Resent-By
bayes_ignore_header X-Resent-To
bayes_ignore_header Resent-To
bayes_ignore_header Sender
bayes_ignore_header Precedence
bayes_ignore_header X-Antispam
bayes_ignore_header X-Sieve
bayes_ignore_header X-Spamcount
bayes_ignore_header X-Spamsensitivity
bayes_ignore_header To
bayes_ignore_header X-Sieve
bayes_ignore_header X-WEBDE-FORWARD
### added lines end ###