It's an SMTP server written in Go, for the purpose of receiving large volumes of email. It started as a project for GuerrillaMail.com which processes millions of emails every day, and needed a daemon with less bloat & written in a more memory-safe language that can take advantage of modern multi-core architectures.
The purpose of this daemon is to grab the email, save it, and disconnect as quickly as possible, essentially performing the services of a Mail Transfer Agent (MTA) without the sending functionality. More Info »
The software also includes a modular backend implementation, which can extend the email processing functionality to whatever needs you may require. We refer to these modules as "Processors". Processors can be chained via the config to perform different tasks on received email, or to validate recipients.
See the list of available Processors below.
For more details about the backend system, see the: Backends, configuring and extending page.