diff --git a/lib/types.ts b/lib/types.ts
index 7e4ffe5..93a0be3 100644
--- a/lib/types.ts
+++ b/lib/types.ts
@@ -35,6 +35,7 @@ export interface EmailAttachment {
   size: number;
   path?: string;
   content?: string;
+  attachmentId?: string; // ID for Microsoft Graph API attachments (used for on-demand fetching)
 }
 
 export interface EmailMessage {