About SproutDNS

SproutDNS is a special-purpose DNS server designed to synthesize responses to DNS queries, allowing more complex behaviour than is possible with a traditional DNS server.

This is useful for publishing tenant-specific DNS data, in particular email authentication records for the situation where there are a large number of tenants being supported in a single DNS domain. As an example, if an email service provider wants to support aligned authentication for a number of tenants who don't own their own domain names in a way that isolates reputation between them. (I discussed this usage in more depth in this blog post.)