diff --git a/client/basic/client.ts b/client/basic/client.ts
index 68713b8..03d6a24 100644
--- a/client/basic/client.ts
+++ b/client/basic/client.ts
@@ -259,6 +259,12 @@ export class SMTPClient {
           "name=" + attachment.filename,
         );
 
+        if (attachment.contentID) {
+          await this.#connection.writeCmd(
+            `Content-ID: <${attachment.contentID}>`,
+          );
+        }
+
         await this.#connection.writeCmd(
           "Content-Disposition: attachment; filename=" + attachment.filename,
         );
diff --git a/config/mail/attachments.ts b/config/mail/attachments.ts
index 9bbe69e..95c9ba3 100644
--- a/config/mail/attachments.ts
+++ b/config/mail/attachments.ts
@@ -3,6 +3,7 @@ import { base64Encode } from "./encoding.ts";
 interface baseAttachment {
   contentType: string;
   filename: string;
+  contentID?: string | number;
 }
 
 export type Attachment =