diff --git a/Keyserver-less-OpenPGP.md b/Keyserver-less-OpenPGP.md
index 8cd888d..356674f 100644
--- a/Keyserver-less-OpenPGP.md
+++ b/Keyserver-less-OpenPGP.md
@@ -1,7 +1,7 @@
 Warning: This does not discuss trust, only key discovery!
 
 # Opportunistic Key Discovery
-  * A: Send normal email with header ``OpenPGP: preference=signencrypt``
+  * A: Send normal email with header ``OpenPGP: preference=signencrypt`` ([see Internet-Draft](https://tools.ietf.org/html/draft-josefsson-openpgp-mailnews-header-07))
   * B: Receiver's parses header and now knows that A can do OpenPGP
   * B: Next normal email is signed and contains the key as attachment
   * A: Email is received, key is automatically imported and signature verified. Check that key corresponds to sig?