Rspamd is an open-source spam filtering and email security engine written in C. It protects mail systems from spam, phishing, business email compromise and malicious attachments, checks sender authentication through SPF, DKIM, DMARC and ARC, and applies content analysis and machine learning. It is delivered as software that organisations run on their own mail infrastructure, and the company also offers commercial plans and a hosted option.
Rspamd is developed by Rspamd Ltd, a company registered in England with its registered office in Cambridge. As a UK company it sits outside the EU and EEA, so hosted services fall under UK jurisdiction. The engine is licensed under Apache 2.0. The company states that with self-hosting, message content stays in the customer's environment. Its website does not state where the Hosted plan's infrastructure is located, and it publishes no data processing agreement. European organisations that want to keep mail content in their own control can run the engine on infrastructure they operate.