Multi line header_checks isn't well documented
In mailman.cfg it says:
[antispam]
# This section defines basic antispam detection settings.
# This value contains lines which specify RFC 822 headers in the email to
# check for spamminess. Each line contains a `key: value` pair, where the key
# is the header to check and the value is a Python regular expression to match
# against the header's value. E.g.:
#
# X-Spam: (yes|maybe)
#
# The header value and regular expression are always matched
# case-insensitively.
But it is not clear how one would enter multiple lines.
Neither of these variants works:
header_checks: X-Spam: (yes|maybe)
header_checks: x-another-header: (some|any)thing
or:
header_checks: X-Spam: (yes|maybe)
x-another-header: (some|any)thing
nor:
header_checks: ['X-Spam: (yes|maybe)', 'x-another-header: (some|any)thing']
p.s. I sent this to mailman-users@mailman3.org as well. But it seems to be out of service today.