Example SPF check and rate limit plugin for Zone-MTA.
Add this as a dependency for your ZoneMTA app
npm installzmta-xauth-ratelimit --save
Assuming you are using configuration format from zone-mta-template create config file plugins/zmta-xauth-ratelimit.toml
# plugins/zmta-xauth-ratelimit.toml
["modules/zmta-xauth-ratelimit"]
enabled=["receiver"]
["modules/zmta-xauth-ratelimit".ratelimits]
minute = 60
day = 1000