diff --git a/crates/jmap/Cargo.toml b/crates/jmap/Cargo.toml
index 8f40ccb..a55745e 100644
--- a/crates/jmap/Cargo.toml
+++ b/crates/jmap/Cargo.toml
@@ -19,6 +19,7 @@ spam-filter = { path = "../spam-filter" }
 email = { path = "../email" }
 groupware = { path = "../groupware" }
 registry = { path = "../registry" }
+inbuxa-features = { path = "../features" }
 calcard = { version = "0.3" }
 smtp-proto = { version = "0.2" }
 mail-parser = { version = "0.11", features = ["full_encoding", "rkyv"] } 
diff --git a/crates/jmap/src/api/auth.rs b/crates/jmap/src/api/auth.rs
index 043411c..110e2d2 100644
--- a/crates/jmap/src/api/auth.rs
+++ b/crates/jmap/src/api/auth.rs
@@ -89,6 +89,11 @@ impl JmapAuthorization for AccessToken {
                     let MethodObject::Registry(object_type) = object else {
                         unreachable!()
                     };
+                    // inbuxa: MT-2: server-level objects are out of a tenant's reach
+                    assert_tenant_reach(
+                        self,
+                        inbuxa_features::tenancy::reach::can_read(object_type),
+                    )?;
                     object_type.get_permission()
                 }
             },
@@ -203,6 +208,11 @@ impl JmapAuthorization for AccessToken {
                         let MethodObject::Registry(object_type) = object else {
                             unreachable!()
                         };
+                        // inbuxa: MT-2, MT-12: server-level objects are out of a tenant's reach
+                        assert_tenant_reach(
+                            self,
+                            inbuxa_features::tenancy::reach::can_write(object_type),
+                        )?;
                         let set_permissions = object_type.set_permission();
                         validate_set(
                             s,
@@ -295,6 +305,11 @@ impl JmapAuthorization for AccessToken {
                     let MethodObject::Registry(object_type) = object else {
                         unreachable!()
                     };
+                    // inbuxa: MT-2: server-level objects are out of a tenant's reach
+                    assert_tenant_reach(
+                        self,
+                        inbuxa_features::tenancy::reach::can_read(object_type),
+                    )?;
                     object_type.query_permission()
                 }
             },
@@ -316,6 +331,17 @@ impl JmapAuthorization for AccessToken {
     }
 }
 
+// inbuxa: MT-2
+fn assert_tenant_reach(access_token: &AccessToken, reachable: bool) -> trc::Result<()> {
+    if reachable || access_token.tenant_id().is_none() {
+        Ok(())
+    } else {
+        Err(trc::JmapEvent::Forbidden
+            .into_err()
+            .details("You are not authorized to perform this action"))
+    }
+}
+
 fn validate_set<T: JmapObject>(
     set: &SetRequest<'_, T>,
     access_token: &AccessToken,
diff --git a/crates/jmap/src/registry/get.rs b/crates/jmap/src/registry/get.rs
index 074eefa..172d512 100644
--- a/crates/jmap/src/registry/get.rs
+++ b/crates/jmap/src/registry/get.rs
@@ -198,6 +198,11 @@ impl RegistryGet for Server {
 
                 let ids = if let Some(ids) = get.ids.take() {
                     ids
+                } else if object_type == ObjectType::Tenant
+                    && let Some(tenant_id) = access_token.tenant_id()
+                {
+                    // inbuxa: MT-12: inside a tenant, only its own tenant object
+                    vec![Id::from(tenant_id)]
                 } else {
                     self.registry()
                         .query::<Vec<Id>>(
@@ -223,6 +228,11 @@ impl RegistryGet for Server {
                                 != object.inner.member_tenant_id())
                             || (is_account_filtered
                                 && object.inner.account_id() != Some(Id::from(get.account_id)))
+                            // inbuxa: MT-12: inside a tenant, only its own tenant object
+                            || (object_type == ObjectType::Tenant
+                                && access_token
+                                    .tenant_id()
+                                    .is_some_and(|tenant_id| tenant_id != id.document_id()))
                         {
                             get.not_found(id);
                             continue;
diff --git a/crates/jmap/src/registry/query.rs b/crates/jmap/src/registry/query.rs
index 22ce60f..6e773aa 100644
--- a/crates/jmap/src/registry/query.rs
+++ b/crates/jmap/src/registry/query.rs
@@ -265,6 +265,14 @@ impl RegistryQuery for Server {
                     }
                 };
 
+                // inbuxa: MT-12: inside a tenant, only its own tenant object
+                let mut results = results;
+                if object_type == ObjectType::Tenant
+                    && let Some(tenant_id) = access_token.tenant_id()
+                {
+                    results.retain(|id| id.document_id() == tenant_id);
+                }
+
                 // Build response
                 let mut response = QueryResponseBuilder::new(
                     results.len(),
diff --git a/crates/jmap/src/registry/set.rs b/crates/jmap/src/registry/set.rs
index cc90454..dc83811 100644
--- a/crates/jmap/src/registry/set.rs
+++ b/crates/jmap/src/registry/set.rs
@@ -381,6 +381,15 @@ impl RegistrySet for Server {
                             new_object.inner.set_member_tenant_id(tenant_id.into());
                         }
 
+                        // inbuxa: MT-7: a principal takes its domain's tenant
+                        if can_set_tenant {
+                            inbuxa_features::tenancy::writes::default_tenant(
+                                self.registry(),
+                                &mut new_object,
+                            )
+                            .await?;
+                        }
+
                         // Add accountId
                         if has_account_id {
                             new_object.inner.set_account_id(set.account_id.into());
@@ -526,6 +535,26 @@ impl RegistrySet for Server {
                         }
                     };
 
+                    // inbuxa: MT-3, MT-8, MT-17
+                    let (stored_id, stored) = match &modification {
+                        Modification::Update { id, object } => (Some(*id), Some(object)),
+                        Modification::Create { .. } => (None, None),
+                    };
+                    let after_save = match inbuxa_features::tenancy::writes::check(
+                        self.registry(),
+                        stored_id,
+                        stored,
+                        &new_object,
+                    )
+                    .await?
+                    {
+                        Ok(after_save) => after_save,
+                        Err(err) => {
+                            set.failed(modification, err);
+                            continue 'outer;
+                        }
+                    };
+
                     // Validate expressions
                     if let Some(expressions) = new_object.inner.expression_ctxs() {
                         let mut bp = Bootstrap::new_uninitialized(self.registry().clone());
@@ -590,6 +619,16 @@ impl RegistrySet for Server {
                     let object_id = match (modification, result) {
                         (Modification::Update { id, object }, RegistryWriteResult::Success(_)) => {
                             cache_invalidator.process_update(id, &object, &new_object);
+                            // inbuxa: MT-8: what moves with a domain follows it
+                            for (id, old, new) in inbuxa_features::tenancy::writes::after_save(
+                                &self.core.storage.data,
+                                self.registry(),
+                                after_save,
+                            )
+                            .await?
+                            {
+                                cache_invalidator.process_update(id, &old, &new);
+                            }
                             if let (
                                 ObjectInner::Application(previous),
                                 ObjectInner::Application(updated),