A European email certification program operated by eco — Association of the Internet Industry. Senders who participate agree to comply with strict anti-spam and deliverability best practices, including proper list hygiene, authentication, and complaint handling.
CSA-certified senders include a X-CSA-Complaints header pointing to csa-complaints@eco.de, giving recipients and ISPs a standardized channel for reporting abuse. Certification signals to mailbox providers that the sender has been vetted, which can improve inbox placement across participating European ISPs.