Hi there,
I'm pleased to advise that rate limiting of password reset request emails has been implemented in the upcoming v9.0 release.

Version 9.0 is currently undergoing public pre-release testing. Please use this opportunity to test it out and share your feedback with us: https://whmcs.community/forum/660-whmcs-90-rc-discussion/

Feature Documentation: https://docs.whmcs.com/releases/9-0/9-0-release-notes/#rate-limiting-for-user-login-attempts

To learn more about the latest release and to take part in pre-release testing, visit https://preview.whmcs.com