This is used by root to look up emails in Mandrill. It might be able to be replaced by calls to Rumi, but that effort has not been scoped or prioritized at this time.
A Ruby API client for the Mandrill email as a service product.
https://bitbucket.org/mailchimp/mandrill-api-ruby
https://rubygems.org/gems/mandrill-api
https://mandrillapp.com/api/docs/index.ruby.html
The Mandrill-api gem doesn't have any update since 2015, this is a fork of such API which relays on JSON V2 rather than V1.