diff --git a/mail.php b/mail.php
index 581a943..4681506 100644
--- a/mail.php
+++ b/mail.php
@@ -1314,7 +1314,7 @@ class mail
     $data = openssl_random_pseudo_bytes (16);
     $data[6] = chr(ord($data[6]) & 0x0f | 0x40); // set version to 0010
     $data[8] = chr(ord($data[8]) & 0x3f | 0x80); // set bits 6-7 to 10
-    return "-----=_".vsprintf ('%s%s-%s-%s-%s-%s%s%s',
+    return "-----".vsprintf ('%s%s%s%s%s%s%s%s',
                                str_split (bin2hex ($data), 4));
   }