email-via-mail-system

name	email-via-mail-system
description	Describe how the filesystem-first mailbox protocol maps to a future true email system while staying semantically compatible. Use when Codex needs header mapping, reserved env-name guidance, or compatibility checks for a future mail-system adapter; do not use it as an implementation skill for this change.

Email Via Mail System

Overview

Use this skill to reason about how the filesystem-first mailbox protocol should map to a future true email system. This change does not implement that transport, so treat this skill as compatibility guidance rather than an operational runtime workflow.

References

• Read references/env-vars.md when checking reserved future env names for a mail-system adapter.
• Read references/email-headers.md when you need exact header mapping or canonical threading rules for future true-email adaptation.

Compatibility Checks

• Use the reserved common and mail-system-compatible env names defined in references/env-vars.md when documenting or designing a future adapter.
• Do not assume those AGENTSYS_MAILBOX_EMAIL_* env vars are populated by the current runtime implementation in this change.

Compatibility Rules

• Keep the canonical mailbox semantics primary and treat true-email fields as an adaptation layer.
• Preserve canonical reply ancestry using standard headers such as Message-ID, In-Reply-To, and References.
• Preserve canonical thread_id through explicit protocol metadata rather than subject-line heuristics.
• Keep the body Markdown-compatible and preserve attachment reference metadata so a future adapter can normalize back into the canonical mailbox model.
• Use the exact mapping rules in references/email-headers.md instead of inventing mail-only semantics.

Guardrails

• Do not claim that this change implements a working mail server, SMTP adapter, or IMAP adapter.
• Do not hardcode SMTP or IMAP hosts, ports, or mailbox addresses into instructions, prompts, or generated files.
• Do not use subject lines alone to determine thread identity.
• Do not drop canonical attachment reference metadata just because the transport is a real mail service.
• Do not treat reserved AGENTSYS_MAILBOX_EMAIL_* names as currently populated runtime bindings unless a future change explicitly implements them.