DBMail is an open-source message delivery agent that uses industry-standard protocols like IMAP, POP, ManageSieve, and LMTP. It stores emails in databases such as PostgreSQL, MySQL, and Oracle, providing a scalable and secure solution for managing user emails. DBMail is designed to integrate with existing authentication backends like ActiveDirectory and OpenLDAP, making it suitable for large-scale deployments. It supports features like email filtering using SIEVE and offers high availability through database replication and Docker images.