email-via-mail-system

To map mailbox protocol headers to true email transport fields, you map canonical fields like message_id and thread_id onto standard email headers such as Message-ID, In-Reply-To, References, and X-Agent-Thread-ID using explicit rules. This ensures canonical threading and ancestry are preserved during the adaptation.

The AGENTSYS_MAILBOX_EMAIL_* environment variable names are explicitly reserved for future email adapter compatibility. You must treat these bindings as compatibility placeholders, recognizing they are not guaranteed to be populated by the current runtime environment.

To preserve canonical reply ancestry when switching to email, you must explicitly maintain Message-ID, In-Reply-To, and References headers alongside explicit thread_id protocol metadata. This guarantees the true-email fields act as an adaptation layer without losing the canonical source of truth.

Yes, a filesystem-first mailbox protocol supports round-trip semantic preservation by ensuring true-email fields act purely as an adaptation layer. This approach keeps canonical mailbox semantics as the source of truth, maintaining Markdown-compatible bodies and attachment reference metadata across the translation.

You should not use true email headers as the canonical source for message threading when designing a future adapter. Canonical mailbox semantics must remain the source of truth, with email headers serving only as an adaptation layer to prevent losing identity or threading data.

The best way to verify a future mail-system adapter is to check it against exact header mapping rules and guardrails. This ensures the adapter remains semantically compatible with the canonical mailbox protocol, preserving message identity, threading, and attachment metadata.