diff --git a/src/composables/useMailSync.ts b/src/composables/useMailSync.ts
index 3e086d9..7af5163 100644
--- a/src/composables/useMailSync.ts
+++ b/src/composables/useMailSync.ts
@@ -5,10 +5,11 @@
  */
 
 import { ref, onMounted, onUnmounted } from 'vue';
+import type { Ref } from 'vue';
 import { useEntitiesStore } from '../stores/entitiesStore';
 import { useCollectionsStore } from '../stores/collectionsStore';
 
-interface SyncSource {
+export interface SyncSource {
   provider: string;
   service: string | number;
   collections: (string | number)[];
@@ -23,7 +24,21 @@ interface SyncOptions {
   fetchDetails?: boolean;
 }
 
-export function useMailSync(options: SyncOptions = {}) {
+export interface MailSyncController {
+  isRunning: Ref<boolean>;
+  lastSync: Ref<Date | null>;
+  error: Ref<string | null>;
+  sources: Ref<SyncSource[]>;
+  addSource: (source: SyncSource) => void;
+  removeSource: (source: SyncSource) => void;
+  clearSources: () => void;
+  sync: () => Promise<void>;
+  start: () => void;
+  stop: () => void;
+  restart: () => void;
+}
+
+export function useMailSync(options: SyncOptions = {}): MailSyncController {
   const {
     interval = 30000,
     autoStart = true,
diff --git a/src/stores/collectionsStore.ts b/src/stores/collectionsStore.ts
index 4071292..8d361d9 100644
--- a/src/stores/collectionsStore.ts
+++ b/src/stores/collectionsStore.ts
@@ -9,8 +9,13 @@ import { CollectionObject, CollectionPropertiesObject } from '../models/collecti
 import type { SourceSelector, ListFilter, ListSort } from '../types'
 
 export const useCollectionsStore = defineStore('mailCollectionsStore', () => {
+  const ROOT_IDENTIFIER = '__root__'
+  const SERVICE_INDEX_IDENTIFIER = '__service__'
+
   // State
   const _collections = ref<Record<string, CollectionObject>>({})
+  const _collectionsByServiceIndex = ref<Record<string, string[]>>({})
+  const _collectionsByParentIndex = ref<Record<string, string[]>>({})
   const transceiving = ref(false)
 
   /**
@@ -33,13 +38,20 @@ export const useCollectionsStore = defineStore('mailCollectionsStore', () => {
    */
   const collectionsByService = computed(() => {
     const groups: Record<string, CollectionObject[]> = {}
-    
-    Object.values(_collections.value).forEach((collection) => {
-      const serviceKey = `${collection.provider}:${collection.service}`
-      if (!groups[serviceKey]) {
-        groups[serviceKey] = []
+
+    Object.keys(_collectionsByServiceIndex.value).forEach(serviceIndexKey => {
+      const collectionKeys = _collectionsByServiceIndex.value[serviceIndexKey] ?? []
+      const collectionsForKey = collectionKeys
+        .map(collectionKey => _collections.value[collectionKey])
+        .filter((collection): collection is CollectionObject => collection !== undefined)
+
+      if (collectionsForKey.length === 0) {
+        return
       }
-      groups[serviceKey].push(collection)
+
+      const firstCollection = collectionsForKey[0]
+      const serviceKey = `${firstCollection.provider}:${firstCollection.service}`
+      groups[serviceKey] = collectionsForKey
     })
     
     return groups
@@ -75,10 +87,9 @@ export const useCollectionsStore = defineStore('mailCollectionsStore', () => {
    * @returns Array of collection objects
    */
   function collectionsForService(provider: string, service: string | number, retrieve: boolean = false): CollectionObject[] {
-    const serviceKeyPrefix = `${provider}:${service}:`
-    const serviceCollections = Object.entries(_collections.value)
-      .filter(([key]) => key.startsWith(serviceKeyPrefix))
-      .map(([_, collection]) => collection)
+    const serviceCollections = collectionObjectsForKeys(
+      _collectionsByServiceIndex.value[identifierKey(provider, service, SERVICE_INDEX_IDENTIFIER)] ?? [],
+    )
     
     if (retrieve === true && serviceCollections.length === 0) {
       console.debug(`[Mail Manager][Store] - Force fetching collections for service "${provider}:${service}"`)
@@ -93,19 +104,26 @@ export const useCollectionsStore = defineStore('mailCollectionsStore', () => {
     return serviceCollections
   }
 
-  function collectionsInCollection(provider: string, service: string | number, collectionId: string | number, retrieve: boolean = false): CollectionObject[] {
-    const collectionKeyPrefix = `${provider}:${service}:${collectionId}:`
-    const nestedCollections = Object.entries(_collections.value)
-      .filter(([key]) => key.startsWith(collectionKeyPrefix))
-      .map(([_, collection]) => collection)
+  /**
+   * Get direct child collections for a parent collection, or root collections when parent is null.
+   *
+   * @param provider - provider identifier
+   * @param service - service identifier
+   * @param collectionId - parent collection identifier, or null for root-level collections
+   * @param retrieve - Retrieve behavior: true = fetch service collections if missing, false = cache only
+   *
+   * @returns Array of direct child collection objects
+   */
+  function collectionsInCollection(provider: string, service: string | number, collectionId: string | number | null, retrieve: boolean = false): CollectionObject[] {
+    const nestedCollections = collectionObjectsForKeys(
+      _collectionsByParentIndex.value[identifierKey(provider, service, collectionId)] ?? [],
+    )
     
     if (retrieve === true && nestedCollections.length === 0) {
       console.debug(`[Mail Manager][Store] - Force fetching collections in collection "${provider}:${service}:${collectionId}"`)
       const sources: SourceSelector = {
         [provider]: {
-          [String(service)]: {
-            [String(collectionId)]: true
-          }
+          [String(service)]: true
         }
       }
       list(sources)
@@ -114,11 +132,66 @@ export const useCollectionsStore = defineStore('mailCollectionsStore', () => {
     return nestedCollections
   }
 
+  function hasChildrenInCollection(provider: string, service: string | number, collectionId: string | number | null): boolean {
+    return (_collectionsByParentIndex.value[identifierKey(provider, service, collectionId)]?.length ?? 0) > 0
+  }
+
   /**
    * Create unique key for a collection
    */
   function identifierKey(provider: string, service: string | number | null, identifier: string | number | null): string {
-    return `${provider}:${service ?? ''}:${identifier ?? ''}`
+    return `${provider}:${String(service ?? ROOT_IDENTIFIER)}:${String(identifier ?? ROOT_IDENTIFIER)}`
+  }
+
+  function collectionObjectsForKeys(collectionKeys: string[]): CollectionObject[] {
+    return collectionKeys
+      .map(collectionKey => _collections.value[collectionKey])
+      .filter((collection): collection is CollectionObject => collection !== undefined)
+  }
+
+  function addIndexEntry(index: Record<string, string[]>, indexKey: string, collectionKey: string) {
+    const existing = index[indexKey] ?? []
+
+    if (existing.includes(collectionKey)) {
+      return
+    }
+
+    index[indexKey] = [...existing, collectionKey]
+  }
+
+  function removeIndexEntry(index: Record<string, string[]>, indexKey: string, collectionKey: string) {
+    const existing = index[indexKey]
+
+    if (!existing) {
+      return
+    }
+
+    const filtered = existing.filter(existingKey => existingKey !== collectionKey)
+
+    if (filtered.length === 0) {
+      delete index[indexKey]
+      return
+    }
+
+    index[indexKey] = filtered
+  }
+
+  function indexCollection(collection: CollectionObject) {
+    const collectionKey = identifierKey(collection.provider, collection.service, collection.identifier)
+    const serviceIndexKey = identifierKey(collection.provider, collection.service, SERVICE_INDEX_IDENTIFIER)
+    const parentIndexKey = identifierKey(collection.provider, collection.service, collection.collection)
+
+    addIndexEntry(_collectionsByServiceIndex.value, serviceIndexKey, collectionKey)
+    addIndexEntry(_collectionsByParentIndex.value, parentIndexKey, collectionKey)
+  }
+
+  function deindexCollection(collection: CollectionObject) {
+    const collectionKey = identifierKey(collection.provider, collection.service, collection.identifier)
+    const serviceIndexKey = identifierKey(collection.provider, collection.service, SERVICE_INDEX_IDENTIFIER)
+    const parentIndexKey = identifierKey(collection.provider, collection.service, collection.collection)
+
+    removeIndexEntry(_collectionsByServiceIndex.value, serviceIndexKey, collectionKey)
+    removeIndexEntry(_collectionsByParentIndex.value, parentIndexKey, collectionKey)
   }
 
   // Actions
@@ -143,6 +216,12 @@ export const useCollectionsStore = defineStore('mailCollectionsStore', () => {
         Object.entries(providerServices).forEach(([_serviceId, serviceCollections]) => {
           Object.entries(serviceCollections).forEach(([_collectionId, collectionObj]) => {
             const key = identifierKey(collectionObj.provider, collectionObj.service, collectionObj.identifier)
+            const previousCollection = _collections.value[key]
+
+            if (previousCollection) {
+              deindexCollection(previousCollection)
+            }
+
             collections[key] = collectionObj
           })
         })
@@ -150,6 +229,9 @@ export const useCollectionsStore = defineStore('mailCollectionsStore', () => {
 
       // Merge retrieved collections into state
       _collections.value = { ..._collections.value, ...collections }
+      Object.values(collections).forEach(collectionObj => {
+        indexCollection(collectionObj)
+      })
 
       console.debug('[Mail Manager][Store] - Successfully retrieved', Object.keys(collections).length, 'collections')
       return collections
@@ -177,7 +259,14 @@ export const useCollectionsStore = defineStore('mailCollectionsStore', () => {
       
       // Merge fetched collection into state
       const key = identifierKey(response.provider, response.service, response.identifier)
+      const previousCollection = _collections.value[key]
+
+      if (previousCollection) {
+        deindexCollection(previousCollection)
+      }
+
       _collections.value[key] = response
+      indexCollection(response)
 
       console.debug('[Mail Manager][Store] - Successfully fetched collection:', key)
       return response
@@ -234,6 +323,7 @@ export const useCollectionsStore = defineStore('mailCollectionsStore', () => {
       // Merge created collection into state
       const key = identifierKey(response.provider, response.service, response.identifier)
       _collections.value[key] = response
+      indexCollection(response)
       
       console.debug('[Mail Manager][Store] - Successfully created collection:', key)
       return response
@@ -267,7 +357,14 @@ export const useCollectionsStore = defineStore('mailCollectionsStore', () => {
       
       // Merge updated collection into state
       const key = identifierKey(response.provider, response.service, response.identifier)
+      const previousCollection = _collections.value[key]
+
+      if (previousCollection) {
+        deindexCollection(previousCollection)
+      }
+
       _collections.value[key] = response
+      indexCollection(response)
       
       console.debug('[Mail Manager][Store] - Successfully updated collection:', key)
       return response
@@ -295,6 +392,12 @@ export const useCollectionsStore = defineStore('mailCollectionsStore', () => {
       
       // Remove deleted collection from state
       const key = identifierKey(provider, service, identifier)
+      const previousCollection = _collections.value[key]
+
+      if (previousCollection) {
+        deindexCollection(previousCollection)
+      }
+
       delete _collections.value[key]
 
       console.debug('[Mail Manager][Store] - Successfully deleted collection:', key)
@@ -317,6 +420,7 @@ export const useCollectionsStore = defineStore('mailCollectionsStore', () => {
     collectionsByService,
     collectionsForService,
     collectionsInCollection,
+    hasChildrenInCollection,
     // Actions
     collection,
     list,