SpamAssassin as a Docker image. It runs spamd on exposed port 783 and
constantly updates its ruleset.
docker run -d -p 783:783 sstraus/docker-spamassassin
or linked (this is how I use it)
docker run -d --name spamassassin sstraus/docker-spamassassin
docker run -d --link spamassassin:spamassassin application-with-spamc-or-something