Why AI email agents need an immutable audit log outside the mailbox

As AI agents gain the ability to send emails autonomously, security and compliance teams require a verifiable, tamper-proof record of every message sent or received. The core problem is that a live mailbox is mutable — messages can be moved, deleted, or expire under retention limits, making it unsuitable as an audit trail. The recommended architecture separates the live mailbox from an append-only audit store keyed by message ID, where records are never updated or deleted. Developers can capture outbound messages via send-response data and inbound messages via webhooks, then store both in a write-once system such as a WORM object store or hash-chained log. This design ensures that if a customer dispute or regulatory inquiry arises, a defensible and complete communication record exists independently of the agent's mailbox.