use chunkedPassthrough when passing chunks to mailsplit splitter

Author: NickOvt

lib/mail-drop.js

@@ -110,7 +110,7 @@ class MailDrop {
             });
         };
 
-        let raw = new PassThrough();
+        let raw = new mailsplit.ChunkedPassthrough();
         let splitter = new mailsplit.Splitter({
             ignoreEmbedded: true,
             maxHeadSize: MAX_HEAD_SIZE