dnsrbl

make sure the DNSRBL lists you are targeting are still alive. the test can be done according to the very specific RBL mechanism and using generic listing.

from the MX itself!

for zone in \
    bl.spamcop.net \
    public.sarbl.org \
    cbl.abuseat.org \
    psbl.surriel.com \
    db.wpbl.info \
    b.barracudacentral.org \
    bl.blocklist.de \
    spam.spamrats.com \
    truncate.gbudb.net \
    dnsbl.dronebl.org \
    zen.spamhaus.org \
    ; do
    echo $zone
    host 2.0.0.127.$zone && echo OK || echo NOK
    echo
done; unset zone

    # down
    ix.dnsbl.manitu.net \
    dnsbl.inps.de \

some notes about too restrictive lists

# this sometimes blocks gmail...
#   dnsbl.dronebl.org

# this blocks hh.ru
#        truncate.gbudb.net

# this blocks nine.pairlist.net / hackrf-dev-bounces@greatscottgadgets.com
#       spam.spamrats.com

# those block orange.fr...
#       dnsbl.sorbs.net
#       dnsbl-1.uceprotect.net
# http://www.uceprotect.net/en/index.php?m=6&s=11

# apews is blocking online.net ip range
#       l2.apews.org

# this is too restrictive
#       reject_rhsbl_sender dsn.rfc-clueless.org

those are closed

# The RFC-Ignorant.org DNS lists are closed effective 2012-10-30.
#       reject_rhsbl_sender bogusmx.rfc-ignorant.org,
#       reject_rhsbl_sender dsn.rfc-ignorant.org,