diff --git a/src/components/MessageReader.vue b/src/components/MessageReader.vue
index 3a11cb8..0467ffc 100644
--- a/src/components/MessageReader.vue
+++ b/src/components/MessageReader.vue
@@ -1,9 +1,11 @@
 <script setup lang="ts">
 import { computed, ref, watch } from 'vue'
 import { useUser } from '@KTXC'
+import { useMailUiStore } from '@/stores/mailUiStore'
 import type { EntityObject, MessageObject } from '@MailManager/models'
 import { SecurityLevel } from '@/utile/emailSanitizer'
-import { useMailUiStore } from '@/stores/mailUiStore'
+import { mediaViewerCanDisplay, mediaViewerComponent } from '@/services/mediaViewer'
+import type { MediaViewerItem } from '@/types/mediaViewer'
 import ReaderEmpty from './reader/ReaderEmpty.vue'
 import ReaderToolbar from './reader/ReaderToolbar.vue'
 import ReaderHeader from './reader/ReaderHeader.vue'
@@ -28,10 +30,14 @@ const emit = defineEmits<{
 const { getSetting } = useUser()
 const mailUiStore = useMailUiStore()
 
-// Per-message overrides
+// Security overrides
 const allowImages = ref(false)
 const overrideSecurityLevel = ref<SecurityLevel | null>(null)
 
+// Viewer state
+const showViewer = ref(false)
+const viewerIndex = ref(0)
+
 // Computed
 const message = computed<MessageObject | null>(() => {
   return props.entity?.properties ?? null
@@ -55,12 +61,35 @@ const effectiveSecurityLevel = computed(() => {
   return overrideSecurityLevel.value ?? securityLevel.value
 })
 
+// Preview state
+const previewDialog = computed(() => mediaViewerComponent('dialog'))
+const previewItems = computed<MediaViewerItem[]>(() => {
+  const attachments = message.value?.attachments ?? []
+  const items: MediaViewerItem[] = []
+  attachments.forEach((attachment, index) => {
+    if (!mediaViewerCanDisplay(attachment.type)) return
+    items.push({
+      id: attachment.partId || attachment.blobId || attachment.cid || `att-${index}`,
+      title: attachment.name || 'Attachment',
+      mime: attachment.type || '',
+      size: attachment.size ?? null,
+      meta: { index, attachment },
+    })
+  })
+  return items
+})
+
 // Reset overrides when message changes
 watch(() => props.entity, () => {
   allowImages.value = allowImagesDefault.value
   overrideSecurityLevel.value = null
 })
 
+// Close the viewer when switching messages.
+watch(() => props.entity, () => {
+  showViewer.value = false
+})
+
 // Toggle images for current message only
 const toggleImages = () => {
   allowImages.value = !allowImages.value
@@ -113,6 +142,22 @@ const handleFlag = () => {
 const handleCompose = () => {
   emit('compose')
 }
+
+const handlePreview = (index: number) => {
+  const pos = previewItems.value.findIndex(item => item.meta.index === index)
+  if (pos < 0) return
+  viewerIndex.value = pos
+  showViewer.value = true
+}
+
+const handleViewerRetrieve = (item: MediaViewerItem): Promise<Blob> => {
+  if (!props.entity) return Promise.reject(new Error('No message selected'))
+  return mailUiStore.attachmentBlob(props.entity, item.meta.attachment)
+}
+
+const handleViewerDownload = (item: MediaViewerItem) => {
+  if (props.entity) mailUiStore.downloadMessage(props.entity, item.meta.index)
+}
 </script>
 
 <template>
@@ -135,7 +180,7 @@ const handleCompose = () => {
         @move="handleMove"
         @delete="handleDelete"
         @flag="handleFlag"
-        @download="handleDownload()"
+        @download="handleDownload"
         @toggle-images="toggleImages"
         @set-security-level="setSecurityLevel"
       />
@@ -144,7 +189,8 @@ const handleCompose = () => {
       <div class="message-content">
         <ReaderHeader
           :entity="props.entity"
-          @download-attachment="handleDownload"
+          @download="handleDownload"
+          @preview="handlePreview"
         />
         
         <v-divider />
@@ -155,6 +201,19 @@ const handleCompose = () => {
           :allow-images="allowImages"
         />
       </div>
+
+      <!-- Inline attachment viewer (provided by the media_viewer module) -->
+      <component
+        :is="previewDialog"
+        v-if="previewDialog"
+        v-model="showViewer"
+        :items="previewItems"
+        :index="viewerIndex"
+        :source="handleViewerRetrieve"
+        :download="handleViewerDownload"
+        :navigation="true"
+        @update:index="viewerIndex = $event"
+      />
     </template>
   </div>
 </template>
diff --git a/src/components/reader/ReaderHeader.vue b/src/components/reader/ReaderHeader.vue
index 4c04f30..0c7a826 100644
--- a/src/components/reader/ReaderHeader.vue
+++ b/src/components/reader/ReaderHeader.vue
@@ -2,7 +2,18 @@
 import { computed } from 'vue'
 import RecipientDetails from '@/components/common/RecipientDetails.vue'
 import { formatFileSize } from '@/utile/format'
+import { mediaViewerCanDisplay, mediaViewerComponent } from '@/services/mediaViewer'
+import { useMailUiStore } from '@/stores/mailUiStore'
 import type { EntityObject } from '@MailManager/models';
+import type { MessagePartInterface } from '@MailManager/types/message';
+
+interface AttachmentItem {
+  id: string
+  title: string
+  mime: string
+  size?: number | null
+  meta: { index: number; attachment: MessagePartInterface }
+}
 
 interface Props {
   entity: EntityObject | null
@@ -11,9 +22,13 @@ interface Props {
 const props = defineProps<Props>()
 
 const emit = defineEmits<{
-  downloadAttachment: [index: number]
+  download: [index: number]
+  preview: [index: number]
 }>()
 
+const mailUiStore = useMailUiStore()
+const previewPopover = computed(() => mediaViewerComponent('popover'))
+
 const message = computed(() => {
   return props.entity?.properties ?? null
 })
@@ -22,6 +37,33 @@ const randomKey = computed(() => {
   return Math.random().toString(36).substring(2, 15)
 })
 
+const attachmentItems = computed<AttachmentItem[]>(() =>
+  (message.value?.attachments ?? []).map((attachment, index) => ({
+    id: attachment.partId || attachment.blobId || attachment.cid || `att-${index}`,
+    title: attachment.name || 'Attachment',
+    mime: attachment.type || '',
+    size: attachment.size ?? null,
+    meta: { index, attachment },
+  })),
+)
+
+const isPreviewable = (attachment: MessagePartInterface): boolean => {
+  return mediaViewerCanDisplay(attachment.type)
+}
+
+const handleAttachmentClick = (attachment: MessagePartInterface, index: number): void => {
+  if (isPreviewable(attachment)) {
+    emit('preview', index)
+  } else {
+    emit('download', index)
+  }
+}
+
+const handleViewerRetrieve = (item: AttachmentItem): Promise<Blob> => {
+  if (!props.entity) return Promise.reject(new Error('No message selected'))
+  return mailUiStore.attachmentBlob(props.entity, item.meta.attachment)
+}
+
 // Format date for display
 const formatDate = (date: Date | string | null | undefined): string => {
   if (!date) return ''
@@ -37,10 +79,6 @@ const formatDate = (date: Date | string | null | undefined): string => {
     hour12: true
   })
 }
-
-const download = async (index: number): Promise<void> => {
-  emit('downloadAttachment', index)
-}
 </script>
 
 <template>
@@ -101,21 +139,31 @@ const download = async (index: number): Promise<void> => {
       <div class="d-flex flex-wrap gap-2">
         <div
           v-for="(attachment, index) in message?.attachments"
-          :key="randomKey"
+          :key="attachment.partId || attachment.blobId || attachment.cid || index"
           class="attachment-item"
         >
           <v-chip
-            prepend-icon="mdi-paperclip"
+            :prepend-icon="isPreviewable(attachment) ? 'mdi-eye-outline' : 'mdi-paperclip'"
             size="small"
             variant="outlined"
             class="attachment-chip"
-            @click="download(index)"
+            :title="isPreviewable(attachment) ? 'Preview' : 'Download'"
+            @click="handleAttachmentClick(attachment, index)"
           >
             <span class="attachment-name">{{ attachment.name || 'Untitled' }}</span>
             <span v-if="attachment.size != null" class="text-caption text-medium-emphasis ml-1">
               ({{ formatFileSize(attachment.size) }})
             </span>
           </v-chip>
+
+          <!-- Hover preview (provided by the media_viewer module) -->
+          <component
+            :is="previewPopover"
+            v-if="previewPopover && isPreviewable(attachment)"
+            :item="attachmentItems[index]"
+            :source="handleViewerRetrieve"
+            @expand="emit('preview', index)"
+          />
         </div>
       </div>
     </div>
diff --git a/src/services/mediaViewer.ts b/src/services/mediaViewer.ts
new file mode 100644
index 0000000..3472ceb
--- /dev/null
+++ b/src/services/mediaViewer.ts
@@ -0,0 +1,48 @@
+/**
+ * mediaViewer — bridges the Mail UI to the standalone media_viewer module
+ */
+
+import { defineAsyncComponent } from 'vue'
+import { useIntegrationStore } from '@KTXC'
+
+const MEDIA_VIEWER_FORMAT_POINT = 'media_viewer_format'
+const MEDIA_VIEWER_POINT = 'media_viewer'
+
+function mimeMatchesPattern(mime: string, pattern: string): boolean {
+  if (pattern.endsWith('/*')) {
+    return mime.startsWith(pattern.slice(0, -1))
+  }
+  return mime === pattern
+}
+
+function mimeMatchesViewer(mime: string, mimeTypes?: string[], mimePatterns?: string[]): boolean {
+  if (mimeTypes?.includes(mime)) return true
+  if (mimePatterns) {
+    for (const pattern of mimePatterns) {
+      if (mimeMatchesPattern(mime, pattern)) return true
+    }
+  }
+  return false
+}
+
+/** True if a leaf viewer is registered for this MIME type. */
+export function mediaViewerCanDisplay(mime: string | null | undefined): boolean {
+  if (!mime) return false
+  const viewers = useIntegrationStore().getItems(MEDIA_VIEWER_FORMAT_POINT)
+  return viewers.some(viewer =>
+    mimeMatchesViewer(
+      mime,
+      viewer.meta?.mimeTypes as string[] | undefined,
+      viewer.meta?.mimePatterns as string[] | undefined,
+    ),
+  )
+}
+
+export function mediaViewerComponent(type: 'dialog' | 'popover' = 'dialog') {
+  // The integration store prefixes ids with the module handle
+  // (e.g. 'media_viewer.dialog'), so match on the suffix.
+  const entry = useIntegrationStore().getItems(MEDIA_VIEWER_POINT).find(i => i.id.endsWith(`.${type}`))
+  return entry?.component
+    ? defineAsyncComponent(entry.component as () => Promise<unknown>)
+    : null
+}
diff --git a/src/stores/mailStore.ts b/src/stores/mailStore.ts
index 0173efc..3bf52a3 100644
--- a/src/stores/mailStore.ts
+++ b/src/stores/mailStore.ts
@@ -5,7 +5,7 @@ import { useEntitiesStore } from '@MailManager/stores/entitiesStore'
 import { useServicesStore } from '@MailManager/stores/servicesStore'
 import { useMailSync } from '@MailManager/composables/useMailSync'
 import type { ServiceIdentifier, CollectionIdentifier, EntityIdentifier } from '@MailManager/types/common'
-import type { EntityTransmitRequest } from '@MailManager/types/entity'
+import type { EntityTransmitRequest, EntityBlobSelector } from '@MailManager/types/entity'
 import type { MessageAddressInterface, MessageInterface, MessagePartInterface } from '@MailManager/types/message'
 import { ServiceObject, type CollectionObject, type EntityObject } from '@MailManager/models'
 import { CollectionPropertiesObject } from '@MailManager/models/collection'
@@ -571,6 +571,20 @@ export const useMailStore = defineStore('mailStore', () => {
     }
   }
 
+  async function attachmentBlob(entity: EntityObject, part: MessagePartInterface): Promise<Blob> {
+    const selector: EntityBlobSelector = {
+      blobId: part.blobId ?? undefined,
+      partId: part.partId ?? undefined,
+      cid: part.cid ?? undefined,
+    }
+    const results = await entitiesStore.blobs(entity.identifier, [selector])
+    const blob = results[0]?.blob
+    if (!blob) {
+      throw new Error('Attachment content unavailable')
+    }
+    return blob
+  }
+
   // ── Exports ───────────────────────────────────────────────────────────────
 
   return {
@@ -607,6 +621,7 @@ export const useMailStore = defineStore('mailStore', () => {
     deleteFolder,
     moveMessages,
     downloadMessage,
+    attachmentBlob,
     moveFolder,
     renameFolder,
     isServiceFolderLoading,
diff --git a/src/stores/mailUiStore.ts b/src/stores/mailUiStore.ts
index 3cdd25e..69bd494 100644
--- a/src/stores/mailUiStore.ts
+++ b/src/stores/mailUiStore.ts
@@ -710,6 +710,10 @@ export const useMailUiStore = defineStore('mailUiStore', () => {
     }
   }
 
+  function attachmentBlob(entity: EntityObject, part: Parameters<typeof mailStore.attachmentBlob>[1]) {
+    return mailStore.attachmentBlob(entity, part)
+  }
+
   return {
     sidebarVisible,
     settingsDialogVisible,
@@ -758,6 +762,7 @@ export const useMailUiStore = defineStore('mailUiStore', () => {
     flagMessage,
     moveMessages,
     downloadMessage,
+    attachmentBlob,
     messageSelectionModeActivate,
     messageSelectionModeDeactivate,
     messageSelectionToggleOne,
diff --git a/src/types/mediaViewer.ts b/src/types/mediaViewer.ts
new file mode 100644
index 0000000..121665e
--- /dev/null
+++ b/src/types/mediaViewer.ts
@@ -0,0 +1,9 @@
+import type { MessagePartInterface } from "@MailManager/types/message"
+
+export interface MediaViewerItem {
+  id: string
+  title: string
+  mime: string
+  size?: number | null
+  meta: { index: number; attachment: MessagePartInterface }
+}
\ No newline at end of file