there is a missing semicolon that causes rmilter not to start with error:
"config file parse error! line: 156, text: tempdir, reason: syntax error"

which, as expected is the following line

The stock rspamd package provided by Raspbian (jessie) is at version 0.6.10.  The rspamd repository doesn't offer binaries for the armhf architecture (e.g., Raspberry Pi 3) in order to get a more recent package.  Instead, use the yunohost repository for rspamd package (currently at 1.3.5) on armhf.

Use a Unix socket instead of a TCP socket as a Unix socket doesn't play nicely with postfix running
smtpd in a chroot. The author of rmilter recommends using a TCP socket per
https://github.com/vstakhov/rmilter/issues/39

The rmilter package changed the name of its listener service similar to
what was done for rspamd (see commit 2dbc976b).