diff --git a/lib/filter-handler.js b/lib/filter-handler.js
index 05c29947..40ae63c4 100644
--- a/lib/filter-handler.js
+++ b/lib/filter-handler.js
@@ -163,8 +163,8 @@ class FilterHandler {
             });
         }
 
-        prepared.mimeTree.header.unshift('Return-Path: <' + sender + '>');
-        prepared.mimeTree.header.unshift('Delivered-To: ' + recipient);
+        prepared.mimeTree.header.unshift('Return-Path: <' + Buffer.from(sender).toString('binary') + '>');
+        prepared.mimeTree.header.unshift('Delivered-To: ' + Buffer.from(recipient).toString('binary'));
 
         prepared.mimeTree.parsedHeader['return-path'] = '<' + sender + '>';
         prepared.mimeTree.parsedHeader['delivered-to'] = '<' + recipient + '>';