diff --git a/app/exota-milter.py b/app/exota-milter.py
index f2a6284..e622725 100644
--- a/app/exota-milter.py
+++ b/app/exota-milter.py
@@ -229,7 +229,7 @@ class ExOTAMilter(Milter.Base):
               if ar_result.method == 'dkim':
                 if ar_result.result == 'pass':
                   self.passed_dkim_results.append({
-                    "sdid": ar_result.header_d
+                    "sdid": ar_result.header_d.lower()
                   })
                   log_debug(self.mconn_id + "/" + str(self.getsymval('i')) +
                     "/HDR: DKIM passed SDID {0}".format(ar_result.header_d)
diff --git a/tests/miltertest.lua b/tests/miltertest.lua
index de5fecc..7500c45 100644
--- a/tests/miltertest.lua
+++ b/tests/miltertest.lua
@@ -57,7 +57,7 @@ end
 if mt.header(conn, "Authentication-RESULTS", "my-auth-serv-id;\n  dkim=pass header.d=yad.onmicrosoft.comx header.s=selector1-yad-onmicrosoft-com header.b=mmmjFpv8") ~= nil then
   error "mt.header(Subject) failed"  
 end
-if mt.header(conn, "Authentication-RESULTS", "my-auth-serv-id;\n  dkim=pass header.d=chillout2k.de header.s=selector1-yad-onmicrosoft-com header.b=mmmjFpv8") ~= nil then
+if mt.header(conn, "Authentication-RESULTS", "my-auth-serv-id;\n  dkim=pass header.d=Chillout2k.de header.s=selector1-yad-onmicrosoft-com header.b=mmmjFpv8") ~= nil then
   error "mt.header(Subject) failed"  
 end
 if mt.header(conn, "Authentication-Results", "my-auth-serv-id;\n  dkim=fail header.d=yad.onmicrosoft.com header.s=selector2-asdf header.b=mmmjFpv8") ~= nil then