Missed Spam Blocklists (MSBL) is a technology incubator focused on developing tools to help identify and manage spam. Its first project is the Email Blocklist (EBL), a service that lists cryptographic hashes of email addresses found in spam messages. These addresses are often identified in Reply-to headers or message bodies, including in advance-fee fraud and other spam campaigns. The EBL is designed to help recipients contact the senders of spam and can be integrated with email systems and spam filters.

The service supports a range of open-source tools and mail platforms, including SpamAssassin, Fuglu, Postomaat, and Exim. Users can access implementation information and configure compatible software to query the EBL. Its public blocklist is served through dedicated nameservers, while organizations with high query volumes can arrange commercial access through reseller SecurityZones. Some educational and nonprofit users may qualify for discounted or free access. MSBL also publishes project updates and invites contributions, reflecting its role as a developer of blocklist technology and supporting integrations.