An IMAP Agent Framework for Extending Email Functionality in Outsourced Mail Services

This paper presents an organization-managed IMAP Agent framework for extending email functionality in environments that rely on outsourced mail services. In this study, outsourced mail services refer to externally operated mailbox providers offering sufficiently scalable email infrastructures and standard IMAP interfaces, such as Gmail, Microsoft 365, and other commercial mailbox providers. In the proposed framework, IMAP Agents are operated within an organization, while user authentication continues to rely on existing institutional infrastructures such as Identity Providers (IdP) or Integrated Authentication Infrastructure (IAI). The IMAP Agent operates as a post-authentication processing component using credentials issued by these infrastructures, without modifying or intervening in the outsourced mail service itself. The framework enables organization-managed mailbox-side email processing without requiring administrative control over the mail server or dependence on provider-specific APIs. As a proof of concept, representative email-processing functions are implemented, including detection of suspicious messages based on header-level authentication information and automatic insertion of thread-consistent warning messages without altering the original email content. To evaluate the feasibility of the proposed framework, a prototype system was implemented using multiple containerized IMAP Agent instances. The experimental results showed that warning messages were typically appended within approximately 300 ms after message detection. Multi-container evaluations ranging from 1 to 100 concurrent IMAP Agent instances demonstrated low CPU overhead and approximately linear memory growth under idle-monitoring conditions, indicating the operational feasibility of deploying multiple IMAP Agent instances on a single host. These results suggest that the proposed framework can provide provider-independent and organization-managed extension of email functionality in outsourced mail environments through standard IMAP operations.