diff --git a/src/govoplan_core/core/postbox.py b/src/govoplan_core/core/postbox.py
index b306b4c..3b11e27 100644
--- a/src/govoplan_core/core/postbox.py
+++ b/src/govoplan_core/core/postbox.py
@@ -5,6 +5,8 @@ from dataclasses import dataclass, field
 from datetime import datetime
 from typing import Literal, Protocol, runtime_checkable
 
+from govoplan_core.core.events import EventClassification
+
 
 POSTBOX_MODULE_ID = "postbox"
 CAPABILITY_POSTBOX_DIRECTORY = "postbox.directory"
@@ -14,9 +16,62 @@ CAPABILITY_POSTBOX_DELIVERY = "postbox.delivery"
 CAPABILITY_POSTBOX_EVIDENCE = "postbox.evidence"
 CAPABILITY_POSTBOX_ROUTING = "postbox.routing"
 
-PostboxAction = Literal["discover", "read", "send", "acknowledge", "administer"]
+PostboxAction = Literal[
+    "discover",
+    "read",
+    "send",
+    "reply",
+    "acknowledge",
+    "administer",
+]
 PostboxMessageListState = Literal["all", "unread", "read", "acknowledged"]
 PostboxMessageAvailability = Literal["available", "withdrawn", "expired"]
+PostboxBindingStatus = Literal[
+    "active",
+    "missing",
+    "not_effective",
+    "unit_missing",
+    "unit_inactive",
+    "unit_tenant_mismatch",
+    "function_missing",
+    "function_inactive",
+    "function_tenant_mismatch",
+    "function_reassigned",
+    "directory_unavailable",
+]
+
+POSTBOX_CLASSIFICATIONS: tuple[EventClassification, ...] = (
+    "public",
+    "internal",
+    "confidential",
+    "restricted",
+)
+_POSTBOX_CLASSIFICATION_RANK = {
+    value: rank for rank, value in enumerate(POSTBOX_CLASSIFICATIONS)
+}
+
+
+def normalize_postbox_classification(
+    value: str,
+) -> EventClassification | None:
+    candidate = value.strip().casefold()
+    if candidate not in _POSTBOX_CLASSIFICATION_RANK:
+        return None
+    return candidate  # type: ignore[return-value]
+
+
+def postbox_classification_allows(
+    ceiling: str,
+    content: str,
+) -> bool:
+    normalized_ceiling = normalize_postbox_classification(ceiling)
+    normalized_content = normalize_postbox_classification(content)
+    if normalized_ceiling is None or normalized_content is None:
+        return False
+    return (
+        _POSTBOX_CLASSIFICATION_RANK[normalized_content]
+        <= _POSTBOX_CLASSIFICATION_RANK[normalized_ceiling]
+    )
 
 
 @dataclass(frozen=True, slots=True)
@@ -26,6 +81,9 @@ class PostboxActorRef:
     selected_assignment_id: str | None = None
     acting_for_account_id: str | None = None
     authorized_actions: frozenset[PostboxAction] = frozenset()
+    authorized_classifications: frozenset[EventClassification] = frozenset(
+        {"public", "internal"}
+    )
 
 
 @dataclass(frozen=True, slots=True)
@@ -91,6 +149,9 @@ class PostboxAccessDecisionRef:
     selected_assignment_id: str | None = None
     holder_count: int = 0
     vacant: bool = True
+    classification: str = "internal"
+    classification_allowed: bool = True
+    binding_status: PostboxBindingStatus = "active"
 
 
 @dataclass(frozen=True, slots=True)