diff --git a/lib/Controllers/DefaultController.php b/lib/Controllers/DefaultController.php
index 46e8373..94ee34f 100644
--- a/lib/Controllers/DefaultController.php
+++ b/lib/Controllers/DefaultController.php
@@ -13,6 +13,7 @@ use InvalidArgumentException;
 use KTXC\Http\Response\JsonResponse;
 use KTXC\Http\Response\Response;
 use KTXC\Http\Response\StreamedNdJsonResponse;
+use KTXC\Http\Response\StreamedResponse;
 use KTXC\SessionIdentity;
 use KTXC\SessionTenant;
 use KTXF\Controller\ControllerAbstract;
@@ -31,12 +32,6 @@ use KTXM\MailManager\Manager;
 use Psr\Log\LoggerInterface;
 use Throwable;
 
-/**
- * Default Controller - Unified Mail API
- * 
- * Handles all mail operations in JMAP-style API pattern.
- * Supports both single operations and batches with result references.
- */
 class DefaultController extends ControllerAbstract {
 
     private const ERR_MISSING_PROVIDER = 'Missing parameter: provider';
@@ -168,6 +163,7 @@ class DefaultController extends ControllerAbstract {
             'entity.move' => $this->entityMove($tenantId, $userId, $data),
             'entity.copy' => throw new InvalidArgumentException('Operation not implemented: ' . $operation),
             'entity.transmit' => $this->entityTransmit($tenantId, $userId, $data),
+            'entity.download' => $this->entityDownload($tenantId, $userId, $data),
             
             default => throw new InvalidArgumentException(self::ERR_INVALID_OPERATION . $operation)
         };
@@ -558,14 +554,14 @@ class DefaultController extends ControllerAbstract {
         
         if (is_bool($result)) {
             return [
-                'outcome' => 'deleted'
+                'disposition' => 'deleted'
             ];
         }
 
         if ($result instanceof JsonSerializable) {
             return [
-                'outcome' => 'moved',
-                'data' => $result
+                'disposition' => 'moved',
+                'mutation' => $result
             ];
         }
 
@@ -773,21 +769,21 @@ class DefaultController extends ControllerAbstract {
     }
 
     private function entityDelete(string $tenantId, string $userId, array $data): mixed {
-        if (!isset($data['sources'])) {
-            throw new InvalidArgumentException(self::ERR_MISSING_SOURCES);
+        if (!isset($data['targets'])) {
+            throw new InvalidArgumentException(self::ERR_MISSING_TARGETS);
         }
-        if (!is_array($data['sources'])) {
-            throw new InvalidArgumentException(self::ERR_INVALID_SOURCES);
+        if (!is_array($data['targets'])) {
+            throw new InvalidArgumentException(self::ERR_INVALID_TARGETS);
         }
 
-        $sources = ResourceIdentifiers::fromArray($data['sources']);
-        foreach ($sources as $source) {
-            if (!$source instanceof EntityIdentifier) {
-                throw new InvalidArgumentException('Invalid parameter: sources must contain provider:service:collection:entity identifiers');
+        $targets = ResourceIdentifiers::fromArray($data['targets']);
+        foreach ($targets as $target) {
+            if (!$target instanceof EntityIdentifier) {
+                throw new InvalidArgumentException('Invalid parameter: targets must contain provider:service:collection:entity identifiers');
             }
         }
         
-        return $this->mailManager->entityDelete($tenantId, $userId, ...$sources->all());
+        return $this->mailManager->entityDelete($tenantId, $userId, ...$targets->all());
     }
 
     private function entityPatch(string $tenantId, string $userId, array $data): mixed {
@@ -868,4 +864,46 @@ class DefaultController extends ControllerAbstract {
         return ['jobId' => $jobId];
     }
 
+    private function entityDownload(string $tenantId, string $userId, array $data): mixed {
+        if (!isset($data['target'])) {
+            throw new InvalidArgumentException(self::ERR_MISSING_TARGET);
+        }
+        if (!is_string($data['target'])) {
+            throw new InvalidArgumentException(self::ERR_INVALID_IDENTIFIER);
+        }
+
+        // 'part' is optional — null means full RFC 822 message download
+        $part = isset($data['part']) && is_array($data['part']) ? $data['part'] : null;
+
+        $target = ResourceIdentifier::fromString($data['target']);
+        $logger = $this->logger;
+
+        $result = $this->mailManager->entityDownload($tenantId, $userId, $target, $part);
+
+        $filename       = $result->filename();
+        $asciiFilename  = preg_replace('/[^\x20-\x7E]|[\\\\"]/', '_', $filename);
+        $encodedFilename = rawurlencode($filename);
+        $disposition    = sprintf(
+            'attachment; filename="%s"; filename*=UTF-8\'\'%s',
+            $asciiFilename,
+            $encodedFilename,
+        );
+
+        $responseGenerator = (static function () use ($result, $logger): \Generator {
+            try {
+                yield from $result->stream();
+            } catch (\Throwable $t) {
+                $logger->error('Error streaming entity download', ['exception' => $t]);
+                // Headers already sent — cannot change status code; stop output cleanly
+            }
+        })();
+
+        return new StreamedResponse($responseGenerator, 200, [
+            'Content-Disposition'       => $disposition,
+            'Content-Type'              => $result->mimeType(),
+            'Content-Transfer-Encoding' => 'binary',
+            'Cache-Control'             => 'no-store',
+        ]);
+    }
+
 }
diff --git a/lib/Manager.php b/lib/Manager.php
index 7e87034..d14b094 100644
--- a/lib/Manager.php
+++ b/lib/Manager.php
@@ -20,6 +20,7 @@ use KTXF\Mail\Service\ServiceCollectionMutableInterface;
 use KTXF\Mail\Service\ServiceConfigurableInterface;
 use KTXF\Mail\Service\ServiceEntityMutableInterface;
 use KTXF\Mail\Service\ServiceMutableInterface;
+use KTXF\Resource\BinaryResource;
 use KTXF\Resource\Filter\IFilter;
 use KTXF\Resource\Identifier\CollectionIdentifier;
 use KTXF\Resource\Identifier\EntityIdentifier;
@@ -951,6 +952,13 @@ class Manager {
         }
     }
 
+    public function entityDownload(string $tenantId, string $userId, EntityIdentifier $targetEntity, array|null $targetPart): BinaryResource {
+        // retrieve service
+        $service = $this->serviceFetch($tenantId, $userId, $targetEntity->provider(), $targetEntity->service());
+        // download entity
+        return $service->entityDownload($targetEntity, $targetPart);
+    }
+
     /**
      * Check if messages exist
      *
@@ -1294,5 +1302,4 @@ class Manager {
         return $operationOutcome;
     }
 
-
 }
diff --git a/src/services/entityService.ts b/src/services/entityService.ts
index 77aaa39..be8d211 100644
--- a/src/services/entityService.ts
+++ b/src/services/entityService.ts
@@ -2,7 +2,7 @@
  * Entity management service
  */
 
-import { transceivePost, transceiveStream } from './transceive';
+import { transceivePost, transceiveStream, transceiveDownload } from './transceive';
 import type {
   EntityFetchRequest,
   EntityFetchResponse,
@@ -27,6 +27,7 @@ import type {
   EntityListBulkRequest,
   EntityPatchResponse,
   EntityPatchRequest,
+  EntityDownloadRequest,
 } from '../types/entity';
 import { useIntegrationStore } from '@KTXC/stores/integrationStore';
 import { EntityObject } from '../models';
@@ -110,7 +111,7 @@ export const entityService = {
     
     // Convert response to EntityObject instances
     const list: Record<string, EntityObject> = {};
-    Object.entries(response).forEach(([identifier, entity]) => {
+    Object.entries(response).forEach(([, entity]) => {
       list[entity.identifier] = createEntityObject(entity);
     });
     
@@ -216,6 +217,16 @@ export const entityService = {
   async transmit(request: EntityTransmitRequest): Promise<EntityTransmitResponse> {
     return await transceivePost<EntityTransmitRequest, EntityTransmitResponse>('entity.transmit', request);
   },
+
+  /**
+   * Submit a browser-native attachment download request.
+   *
+   * The backend download endpoint is expected to honor the supplied selector
+   * and respond with an attachment payload rather than JSON.
+   */
+  download(request: EntityDownloadRequest): { transaction: string } {
+    return transceiveDownload<EntityDownloadRequest>('entity.download', request);
+  },
 };
 
 export default entityService;
diff --git a/src/services/transceive.ts b/src/services/transceive.ts
index 7b72413..4a795e0 100644
--- a/src/services/transceive.ts
+++ b/src/services/transceive.ts
@@ -141,3 +141,84 @@ export async function transceiveStream<TRequest, TData>(
 
   return { total };
 }
+
+/**
+ * Submit a browser-native file download request via a top-level form POST.
+ *
+ * This avoids buffering the response body in application-managed JavaScript
+ * memory. The backend is expected to accept form fields where `data` contains
+ * the serialized operation payload and to return an attachment response.
+ */
+export function transceiveDownload<TRequest>(
+  operation: string,
+  data: TRequest,
+  user?: string,
+): { transaction: string } {
+  if (typeof document === 'undefined' || typeof window === 'undefined') {
+    throw new Error('Browser window is not available for download submission');
+  }
+
+  const request: ApiRequest<TRequest> = {
+    version: API_VERSION,
+    transaction: generateTransactionId(),
+    operation,
+    data,
+    user,
+  };
+
+  const form = document.createElement('form');
+  form.method = 'POST';
+  form.action = API_URL;
+  form.target = '_blank';
+  form.style.display = 'none';
+
+  appendHiddenField(form, 'version', String(request.version));
+  appendHiddenField(form, 'transaction', request.transaction);
+  appendHiddenField(form, 'operation', request.operation);
+  appendFormValue(form, 'data', request.data);
+
+  if (request.user) {
+    appendHiddenField(form, 'user', request.user);
+  }
+
+  document.body.appendChild(form);
+  form.submit();
+  form.remove();
+
+  return { transaction: request.transaction };
+}
+
+function appendHiddenField(form: HTMLFormElement, name: string, value: string): void {
+  const input = document.createElement('input');
+  input.type = 'hidden';
+  input.name = name;
+  input.value = value;
+  form.appendChild(input);
+}
+
+function appendFormValue(form: HTMLFormElement, name: string, value: unknown): void {
+  if (value === undefined) {
+    return;
+  }
+
+  if (value === null) {
+    appendHiddenField(form, name, '');
+    return;
+  }
+
+  if (Array.isArray(value)) {
+    value.forEach((item, index) => {
+      appendFormValue(form, `${name}[${index}]`, item);
+    });
+    return;
+  }
+
+  if (typeof value === 'object') {
+    Object.entries(value as Record<string, unknown>).forEach(([key, nestedValue]) => {
+      appendFormValue(form, `${name}[${key}]`, nestedValue);
+    });
+    return;
+  }
+
+  appendHiddenField(form, name, String(value));
+}
diff --git a/src/stores/entitiesStore.ts b/src/stores/entitiesStore.ts
index e838031..c192395 100644
--- a/src/stores/entitiesStore.ts
+++ b/src/stores/entitiesStore.ts
@@ -7,7 +7,8 @@ import { defineStore } from 'pinia'
 import { entityService } from '../services'
 import { EntityObject, MessageObject } from '../models'
 import type {
-  EntityListStreamRequest,
+  EntityBlobSelector,
+  EntityDownloadRequest,
   EntityTransmitRequest,
   EntityTransmitResponse,
 } from '../types/entity'
@@ -18,7 +19,7 @@ import type {
   ListRange,
   ListSort,
 } from '../types/common'
-import type { MessageInterface } from '@/types/message'
+import type { MessageInterface, MessagePartInterface } from '@/types/message'
 
 export const useEntitiesStore = defineStore('mailEntitiesStore', () => {
   // State
@@ -184,15 +185,15 @@ export const useEntitiesStore = defineStore('mailEntitiesStore', () => {
       const response = await entityService.delta({ sources })
       
       // Process delta and update store
-      Object.entries(response).forEach(([provider, providerData]) => {
+      Object.entries(response).forEach(([, providerData]) => {
         // Skip if no changes for provider
         if (providerData === false) return
         
-        Object.entries(providerData).forEach(([service, serviceData]) => {
+        Object.entries(providerData).forEach(([, serviceData]) => {
           // Skip if no changes for service
           if (serviceData === false) return
           
-          Object.entries(serviceData).forEach(([collection, collectionData]) => {
+          Object.entries(serviceData).forEach(([, collectionData]) => {
             // Skip if no changes for collection
             if (collectionData === false) return
             
@@ -474,6 +475,39 @@ export const useEntitiesStore = defineStore('mailEntitiesStore', () => {
     }
   }
 
+  async function download(target: EntityIdentifier, part?: Partial<MessagePartInterface>) {
+    let targetPart: EntityBlobSelector | undefined = undefined
+    if (part && (part.blobId || part.partId || part.cid)) {
+      targetPart = {
+        blobId: part.blobId ?? undefined,
+        partId: part.partId ?? undefined,
+        cid: part.cid ?? undefined,
+      }
+    }
+
+    let filename: string
+    if (part && part.name && part.name.trim().length > 0) {
+      filename = part.name.trim()
+    } else if (part) {
+      filename = `attachment-${part.partId || part.blobId || part.cid || 'unknown'}`
+    } else {
+      filename = 'message.eml'
+    }
+
+    const request: EntityDownloadRequest = {
+      target,
+      part: targetPart,
+      filename,
+    }
+
+    try {
+      entityService.download(request)
+    } catch (error: any) {
+      console.error('[Mail Manager][Store] - Failed to submit attachment download:', error)
+      throw error
+    }
+  }
+
   // Return public API
   return {
     // State (readonly)
@@ -495,5 +529,6 @@ export const useEntitiesStore = defineStore('mailEntitiesStore', () => {
     delta,
     move,
     transmit,
+    download,
   }
 })
diff --git a/src/types/entity.ts b/src/types/entity.ts
index 123ca77..1a306eb 100644
--- a/src/types/entity.ts
+++ b/src/types/entity.ts
@@ -205,4 +205,32 @@ export interface EntityTransmitRequest {
 export interface EntityTransmitResponse {
   id: string;
   status: 'queued' | 'sent';
-}
\ No newline at end of file
+}
+
+/**
+ * Entity Blob Fetch
+ */
+export interface EntityBlobSelector {
+  blobId?: string;
+  partId?: string;
+  cid?: string;
+}
+
+export interface EntityDownloadRequest {
+  target: EntityIdentifier;
+  part?: EntityBlobSelector;
+  filename?: string | null;
+}
+
+export interface EntityBlobsRequest {
+  target: EntityIdentifier;
+  parts: EntityBlobSelector[];
+}
+
+export interface EntityBlobsResult {
+  source: EntityIdentifier;
+  part: EntityBlobSelector;
+  blob: Blob;
+}
+
+export interface EntityBlobsResponse extends Array<EntityBlobsResult> {}
\ No newline at end of file