From v4 Debian's spamassasin is has now dedicated package to provide persistent service:

• spamd

so /etc/default/spamassasin should be converted to /etc/default/spamd

Check if some modules are missing:

spamassassin -D --lint 2>&1 | grep -i failed

sudo apt-get install libencode-detect-perl libnet-libidn-perl \
    libemail-address-xs-perl libmail-dkim-perl libmail-spf-perl \
    libio-socket-ip-perl

sudo apt install libdigest-sha-perl libnet-libidn2-perl libmaxmind-db-reader-perl libmaxmind-db-reader-xs-perl

sudo cpan install IP::Country::DB_File Digest::SHA1 IP::Country::Fast

Register legitimate SMTP server at: dnswl.org Self Service

Problem:

info: auto-whitelist: sql-based get_addr_entry xxxxxx: SQL error: Unknown column 'last_hit' in 'order clause'

Solution:

Configure reputation database (read /usr/share/doc/spamassassin/sql/README.txrep) for mysql, execute /usr/share/doc/spamassassin/sql/txrep_mysql.sql

Problem:

  pts rule name              description
 ---- ---------------------- --------------------------------------------------
  0.0 URIBL_BLOCKED          ADMINISTRATOR NOTICE: The query to URIBL was
                             blocked.  See
                             http://wiki.apache.org/spamassassin/DnsBlocklists#dnsbl-block
                              for more information.
                             [URIs: grinn-global.com]

There are lots of queries to google dns 8.8.8.8, but google responds with NXDomain or ServFail. The same single query works. Probably google blocks bursts of this kind of requests.

Solution:

local.cf

dns_server 127.0.0.1