false positives, tagged_above=0, and spam threshold

[David Newman]

amavisd-new-2.11.0_2,1
spamassassin-3.4.1_12
mysql57-server-5.7.23
iRedMail 0.9.8
iRedAdmin-Pro 2.4.0
FreeBSD 11.2-RELEASE-p2

Greetings. Could use some help in debugging what I suspect is a
configuration issue that's resulting in lots of false positives and
messages incorrectly getting tagged as spam.

A mail server running the packages above has its spam threshold set at
6.0 but is classifying as spam many messages with far lower values, and
including a "tagged_above=0" tag in message headers.

Using an example email scored at 1.105 classified as spam, here are
slightly obfuscated versions of:

- message headers
- amavisd.conf
- local.cf
- the policies defined in the MySQL amavisd.policy table; and
- an amavisd/spamassassin debug log for this email (1544 lines)

These are all available here:

https://pastebin.com/9htv3r5D

The things I've obfuscated are usernames, domains, recipient emails
addresses, the server IP address, and a SQL password. If you need any
other info, please let me know.

Pretty sure (I hope, anyway) this is due to some misconfiguration on my
part and not an amavisd-new or spamassassin bug.

Thanks in advance for clues on further troubleshooting.

dn