Run the following commands to disable the antispam plugin:
mkdir -p /etc/e-smith/templates-custom/etc/dovecot/dovecot.conf/
touch /etc/e-smith/templates-custom/etc/dovecot/dovecot.conf/50spam_training
expand-template /etc/dovecot/dovecot.conf
systemctl stop dovecot.service
systemctl start dovecot.service
To undo:
rm /etc/e-smith/templates-custom/etc/dovecot/dovecot.conf/50spam_training
expand-template /etc/dovecot/dovecot.conf
systemctl stop dovecot.service
systemctl start dovecot.service