diff --git a/src/govoplan_postbox/backend/manifest.py b/src/govoplan_postbox/backend/manifest.py
index b003588..0ebbe9c 100644
--- a/src/govoplan_postbox/backend/manifest.py
+++ b/src/govoplan_postbox/backend/manifest.py
@@ -44,9 +44,11 @@ from govoplan_core.core.postbox import (
     CAPABILITY_POSTBOX_MESSAGES,
     CAPABILITY_POSTBOX_ROUTING,
 )
+from govoplan_core.core.search import SearchSourceProviderRegistration
 from govoplan_core.core.views import ViewSurface
 from govoplan_core.db.base import Base
 from govoplan_postbox.backend.db import models as postbox_models
+from govoplan_postbox.backend.search_source import create_postbox_search_source
 
 
 MODULE_ID = "postbox"
@@ -222,6 +224,7 @@ manifest = ModuleManifest(
         "portal",
         "views",
         "workflow_engine",
+        "search",
     ),
     required_capabilities=(
         CAPABILITY_AUTH_PRINCIPAL_RESOLVER,
@@ -266,9 +269,21 @@ manifest = ModuleManifest(
             version_max_exclusive="2.0.0",
             optional=True,
         ),
+        ModuleInterfaceRequirement(
+            name="search.source",
+            version_min="1.0.0",
+            version_max_exclusive="2.0.0",
+            optional=True,
+        ),
     ),
     permissions=PERMISSIONS,
     role_templates=ROLE_TEMPLATES,
+    search_sources=(
+        SearchSourceProviderRegistration(
+            id="postbox.messages",
+            factory=create_postbox_search_source,
+        ),
+    ),
     nav_items=(
         NavItem(
             path="/postbox",
@@ -363,6 +378,23 @@ manifest = ModuleManifest(
         CAPABILITY_POSTBOX_ROUTING: _configure,
     },
     documentation=(
+        DocumentationTopic(
+            id="postbox.search.messages",
+            title="Search authorized Postbox messages",
+            summary="Expose Postbox subjects and permitted plaintext content to permission-aware platform Search.",
+            body=(
+                "When Search is installed, Postbox contributes message subjects, sender labels, and plaintext "
+                "content only. Ciphertext and key material are never indexed. Every result is tenant-bounded and "
+                "rechecks current function assignment, Postbox binding, classification, acting context, and generic "
+                "read authority without recording a message read. Committed deliveries and message changes update "
+                "the derived index through the durable platform event path."
+            ),
+            layer="configured",
+            documentation_types=("admin", "user"),
+            audience=("administrator", "user", "campaign_manager"),
+            related_modules=("search", "idm", "encryption"),
+            order=34,
+        ),
         DocumentationTopic(
             id="postbox.function-bound-containers",
             title="Function-bound Postboxes",
diff --git a/src/govoplan_postbox/backend/search_source.py b/src/govoplan_postbox/backend/search_source.py
new file mode 100644
index 0000000..36553d1
--- /dev/null
+++ b/src/govoplan_postbox/backend/search_source.py
@@ -0,0 +1,296 @@
+from __future__ import annotations
+
+from collections.abc import Mapping, Sequence
+from urllib.parse import quote
+
+from sqlalchemy import func, select
+from sqlalchemy.orm import Session
+
+from govoplan_core.auth import ApiPrincipal
+from govoplan_core.core.events import PlatformEvent
+from govoplan_core.core.modules import ModuleContext
+from govoplan_core.core.postbox import PostboxActorRef
+from govoplan_core.core.search import (
+    SearchAuthorizationRequest,
+    SearchBackfillPage,
+    SearchBackfillRequest,
+    SearchDocument,
+    SearchIndexChange,
+    SearchResourceReference,
+    SearchResourceType,
+)
+from govoplan_postbox.backend.db.models import (
+    Postbox,
+    PostboxMessage,
+    PostboxRoute,
+)
+from govoplan_postbox.backend.service import PostboxService
+
+
+PROVIDER_ID = "postbox.messages"
+RESOURCE_TYPE = "postbox_message"
+READ_SCOPE = "postbox:postbox:read"
+CONFIDENTIAL_SCOPE = "postbox:classification:confidential"
+RESTRICTED_SCOPE = "postbox:classification:restricted"
+
+
+class PostboxSearchSource:
+    def __init__(self, service: PostboxService) -> None:
+        self.service = service
+
+    def resource_types(self) -> Sequence[SearchResourceType]:
+        return (
+            SearchResourceType(
+                provider_id=PROVIDER_ID,
+                module_id="postbox",
+                resource_type=RESOURCE_TYPE,
+                label="Postbox messages",
+                requires_authorization_recheck=True,
+            ),
+        )
+
+    def backfill(
+        self,
+        session: object,
+        *,
+        request: SearchBackfillRequest,
+    ) -> SearchBackfillPage:
+        _assert_source(request.provider_id, request.resource_type)
+        db = _session(session)
+        statement = (
+            select(PostboxMessage, Postbox)
+            .join(Postbox, Postbox.id == PostboxMessage.postbox_id)
+            .where(
+                PostboxMessage.tenant_id == request.tenant_id,
+                Postbox.tenant_id == request.tenant_id,
+            )
+        )
+        if request.cursor:
+            statement = statement.where(PostboxMessage.id > request.cursor)
+        rows = list(
+            db.execute(
+                statement.order_by(PostboxMessage.id).limit(request.limit + 1)
+            ).all()
+        )
+        has_more = len(rows) > request.limit
+        selected = rows[: request.limit]
+        high_watermark = db.scalar(
+            select(func.max(PostboxMessage.updated_at)).where(
+                PostboxMessage.tenant_id == request.tenant_id
+            )
+        )
+        return SearchBackfillPage(
+            documents=tuple(
+                _document(message, postbox=postbox)
+                for message, postbox in selected
+            ),
+            next_cursor=(
+                selected[-1][0].id if has_more and selected else None
+            ),
+            complete=not has_more,
+            high_watermark=(
+                high_watermark.isoformat()
+                if high_watermark is not None
+                else None
+            ),
+        )
+
+    def authorize(
+        self,
+        session: object,
+        principal: object,
+        *,
+        requests: Sequence[SearchAuthorizationRequest],
+    ) -> Mapping[str, bool]:
+        decisions = {item.reference.key: False for item in requests}
+        if not isinstance(principal, ApiPrincipal) or not principal.has(READ_SCOPE):
+            return decisions
+        actor = _actor(principal)
+        db = _session(session)
+        for item in requests:
+            reference = item.reference
+            if (
+                reference.tenant_id != principal.tenant_id
+                or reference.module_id != "postbox"
+                or reference.resource_type != RESOURCE_TYPE
+            ):
+                continue
+            try:
+                decisions[reference.key] = self.service.can_read_message(
+                    db,
+                    tenant_id=principal.tenant_id,
+                    message_id=reference.resource_id,
+                    actor=actor,
+                )
+            except (RuntimeError, ValueError):
+                decisions[reference.key] = False
+        return decisions
+
+    def index_changes_for_event(
+        self,
+        session: object,
+        *,
+        event: PlatformEvent,
+        delivery_key: str,
+    ) -> Sequence[SearchIndexChange]:
+        if (
+            event.module_id != "postbox"
+            or event.tenant is None
+            or event.resource is None
+            or event.resource.id is None
+            or event.resource.type not in {RESOURCE_TYPE, "postbox_route"}
+        ):
+            return ()
+        db = _session(session)
+        message_id = event.resource.id
+        if event.resource.type == "postbox_route":
+            route = db.get(PostboxRoute, event.resource.id)
+            if (
+                route is None
+                or route.tenant_id != event.tenant.id
+                or route.target_message_id is None
+            ):
+                return ()
+            message_id = route.target_message_id
+        row = db.get(PostboxMessage, message_id)
+        postbox = (
+            db.get(Postbox, row.postbox_id)
+            if row is not None and row.tenant_id == event.tenant.id
+            else None
+        )
+        deleted = (
+            row is None
+            or row.tenant_id != event.tenant.id
+            or postbox is None
+        )
+        cursor = event.event_id
+        document = (
+            None
+            if deleted
+            else _document(row, postbox=postbox, change_cursor=cursor)
+        )
+        reference = SearchResourceReference(
+            tenant_id=event.tenant.id,
+            module_id="postbox",
+            resource_type=RESOURCE_TYPE,
+            resource_id=message_id,
+        )
+        return (
+            SearchIndexChange(
+                change_id=f"{delivery_key}:{PROVIDER_ID}:{message_id}",
+                provider_id=PROVIDER_ID,
+                kind="delete" if deleted else "upsert",
+                reference=reference,
+                source_revision=(
+                    document.source_revision if document is not None else cursor
+                ),
+                cursor=cursor,
+                document=document,
+                occurred_at=event.occurred_at,
+            ),
+        )
+
+
+def create_postbox_search_source(
+    context: ModuleContext,
+) -> PostboxSearchSource:
+    return PostboxSearchSource(PostboxService.from_registry(context.registry))
+
+
+def _actor(principal: ApiPrincipal) -> PostboxActorRef:
+    selected = principal.acting_assignment_id
+    if selected is None and len(principal.function_assignment_ids) == 1:
+        selected = next(iter(principal.function_assignment_ids))
+    classifications = {"public", "internal"}
+    if principal.has(CONFIDENTIAL_SCOPE):
+        classifications.add("confidential")
+    if principal.has(RESTRICTED_SCOPE):
+        classifications.update(("confidential", "restricted"))
+    return PostboxActorRef(
+        account_id=principal.account_id,
+        identity_id=principal.identity_id,
+        selected_assignment_id=selected,
+        acting_for_account_id=principal.acting_for_account_id,
+        authorized_actions=frozenset({"discover", "read"}),
+        authorized_classifications=frozenset(classifications),
+    )
+
+
+def _document(
+    message: PostboxMessage,
+    *,
+    postbox: Postbox,
+    change_cursor: str | None = None,
+) -> SearchDocument:
+    updated_at = message.updated_at or message.created_at
+    body = (
+        message.body_text
+        if message.encryption_profile == "plaintext_v1"
+        and message.body_ciphertext is None
+        else None
+    )
+    tokens = [f"scope:{READ_SCOPE}"]
+    if message.classification == "confidential":
+        tokens.append(f"scope:{CONFIDENTIAL_SCOPE}")
+    elif message.classification == "restricted":
+        tokens.append(f"scope:{RESTRICTED_SCOPE}")
+    return SearchDocument(
+        tenant_id=message.tenant_id,
+        module_id="postbox",
+        provider_id=PROVIDER_ID,
+        resource_type=RESOURCE_TYPE,
+        resource_id=message.id,
+        title=message.subject[:500],
+        url=f"/postbox?messageId={quote(message.id, safe='')}",
+        summary=(message.sender_label or postbox.name)[:4000],
+        body=body[:200_000] if body else None,
+        keywords=tuple(
+            item[:200]
+            for item in (
+                postbox.name,
+                message.status,
+                message.classification,
+                message.producer_module or "",
+            )
+            if item
+        ),
+        visibility="restricted",
+        acl_tokens=tuple(dict.fromkeys(tokens)),
+        metadata={
+            "postbox_id": message.postbox_id,
+            "postbox_name": postbox.name,
+            "status": message.status,
+            "classification": message.classification,
+            "sender_label": message.sender_label,
+            "delivered_at": message.delivered_at.isoformat(),
+            "withdrawn_at": (
+                message.withdrawn_at.isoformat()
+                if message.withdrawn_at
+                else None
+            ),
+            "encrypted": body is None and message.body_ciphertext is not None,
+        },
+        source_revision=f"{message.status}:{updated_at.isoformat()}",
+        change_cursor=change_cursor,
+        source_updated_at=updated_at,
+        requires_authorization_recheck=True,
+    )
+
+
+def _assert_source(provider_id: str, resource_type: str) -> None:
+    if provider_id != PROVIDER_ID or resource_type != RESOURCE_TYPE:
+        raise ValueError("Unsupported Postbox search source.")
+
+
+def _session(value: object) -> Session:
+    if not isinstance(value, Session):
+        raise TypeError("Postbox search requires a SQLAlchemy session.")
+    return value
+
+
+__all__ = [
+    "PROVIDER_ID",
+    "PostboxSearchSource",
+    "RESOURCE_TYPE",
+    "create_postbox_search_source",
+]
diff --git a/src/govoplan_postbox/backend/service.py b/src/govoplan_postbox/backend/service.py
index 625d38a..9f328cd 100644
--- a/src/govoplan_postbox/backend/service.py
+++ b/src/govoplan_postbox/backend/service.py
@@ -845,6 +845,32 @@ class PostboxService:
         )
         return self._message_ref(message, account_id=actor.account_id)
 
+    def can_read_message(
+        self,
+        session: object,
+        *,
+        tenant_id: str,
+        message_id: str,
+        actor: PostboxActorRef,
+    ) -> bool:
+        """Recheck message access without creating a read or denial event."""
+
+        db = _session(session)
+        message = self._get_message(
+            db,
+            tenant_id=tenant_id,
+            message_id=message_id,
+            required=False,
+        )
+        if message is None:
+            return False
+        return self._message_access_decision(
+            db,
+            message=message,
+            actor=actor,
+            action="read",
+        ).allowed
+
     def mark_message(
         self,
         session: object,
diff --git a/tests/test_search_source.py b/tests/test_search_source.py
new file mode 100644
index 0000000..d87f940
--- /dev/null
+++ b/tests/test_search_source.py
@@ -0,0 +1,136 @@
+from __future__ import annotations
+
+from datetime import datetime, timezone
+from types import SimpleNamespace
+import unittest
+
+from sqlalchemy import create_engine
+from sqlalchemy.orm import Session
+
+from govoplan_core.auth import ApiPrincipal
+from govoplan_core.core.access import PrincipalRef
+from govoplan_core.core.search import (
+    SearchAuthorizationRequest,
+    SearchBackfillRequest,
+    SearchResourceReference,
+)
+from govoplan_core.db.base import Base
+from govoplan_postbox.backend.db.models import (
+    Postbox,
+    PostboxAddress,
+    PostboxMessage,
+)
+from govoplan_postbox.backend.search_source import (
+    PROVIDER_ID,
+    RESOURCE_TYPE,
+    PostboxSearchSource,
+)
+
+
+class _AccessService:
+    def __init__(self, allowed: bool = True) -> None:
+        self.allowed = allowed
+
+    def can_read_message(self, session, **kwargs):
+        del session, kwargs
+        return self.allowed
+
+
+class PostboxSearchSourceTests(unittest.TestCase):
+    def setUp(self) -> None:
+        self.engine = create_engine("sqlite://")
+        Base.metadata.create_all(
+            self.engine,
+            tables=(
+                PostboxAddress.__table__,
+                Postbox.__table__,
+                PostboxMessage.__table__,
+            ),
+        )
+        self.session = Session(self.engine)
+        self.session.add_all(
+            (
+                PostboxAddress(
+                    id="address-1",
+                    tenant_id="tenant-1",
+                    address_key="permits",
+                    address="permits@example.test",
+                ),
+                Postbox(
+                    id="postbox-1",
+                    tenant_id="tenant-1",
+                    address_id="address-1",
+                    name="Permit office",
+                ),
+                PostboxMessage(
+                    id="message-1",
+                    tenant_id="tenant-1",
+                    postbox_id="postbox-1",
+                    subject="Permit decision",
+                    body_text=None,
+                    body_ciphertext=b"ciphertext",
+                    encryption_profile="server_envelope_v1",
+                    delivered_at=datetime(2026, 8, 5, tzinfo=timezone.utc),
+                ),
+            )
+        )
+        self.session.commit()
+
+    def tearDown(self) -> None:
+        self.session.close()
+        self.engine.dispose()
+
+    def test_encrypted_content_is_not_indexed_and_access_is_rechecked(self) -> None:
+        source = PostboxSearchSource(_AccessService())  # type: ignore[arg-type]
+        page = source.backfill(
+            self.session,
+            request=SearchBackfillRequest(
+                tenant_id="tenant-1",
+                provider_id=PROVIDER_ID,
+                resource_type=RESOURCE_TYPE,
+                rebuild_id="rebuild-1",
+            ),
+        )
+        self.assertEqual(1, len(page.documents))
+        self.assertIsNone(page.documents[0].body)
+        self.assertNotIn("ciphertext", str(page.documents[0].metadata).casefold())
+        reference = SearchResourceReference(
+            tenant_id="tenant-1",
+            module_id="postbox",
+            resource_type=RESOURCE_TYPE,
+            resource_id="message-1",
+        )
+        request = SearchAuthorizationRequest(reference=reference, source_revision="1")
+        self.assertTrue(
+            source.authorize(
+                self.session,
+                _principal(),
+                requests=(request,),
+            )[reference.key]
+        )
+        denied = PostboxSearchSource(_AccessService(False))  # type: ignore[arg-type]
+        self.assertFalse(
+            denied.authorize(
+                self.session,
+                _principal(),
+                requests=(request,),
+            )[reference.key]
+        )
+
+
+def _principal() -> ApiPrincipal:
+    return ApiPrincipal(
+        principal=PrincipalRef(
+            account_id="account-1",
+            membership_id="user-1",
+            identity_id="identity-1",
+            tenant_id="tenant-1",
+            scopes=frozenset({"postbox:postbox:read"}),
+        ),
+        account=SimpleNamespace(id="account-1"),
+        user=SimpleNamespace(id="user-1"),
+    )
+
+
+if __name__ == "__main__":
+    unittest.main()