diff --git a/Milter/utils.py b/Milter/utils.py
index 2ed5db8..85fd635 100644
--- a/Milter/utils.py
+++ b/Milter/utils.py
@@ -8,6 +8,7 @@ import socket
 import email.errors
 from email.header import decode_header
 import email.base64mime
+import email.utils
 from fnmatch import fnmatchcase
 from binascii import a2b_base64