Option To disable the Real-time Learning
To disable the Real-time learning go to Warden -> Settings -> Learning Settings -> Sieve learning -> uncheck Use IMAP sieve learning and save the page. When the real-time learning is disabled the system will fall back to the Plesk nightly training task instead.
Option to use Redis as the Storage Backend
You have the option of using Redis as the Bayes storage engine instead of MySQL (this should speed up sa-learn). This can be found under Warden -> Settings -> Learning Settings -> Storage Settings. Detailed instructions for how to to switch to Redis can be found here.
Using the Command Line Interface
/usr/local/psa/admin/bin/modules/warden/minion antispam:sievelearning --use_sieve_learning=0
systemctl reload postfix