redirect() documentation: add a note for IIS users
diff --git a/user_guide_src/source/helpers/url_helper.rst b/user_guide_src/source/helpers/url_helper.rst
index 8de7817..1987dfb 100644
--- a/user_guide_src/source/helpers/url_helper.rst
+++ b/user_guide_src/source/helpers/url_helper.rst
@@ -325,3 +325,7 @@
.. note:: For very fine grained control over headers, you should use the
`Output Library </libraries/output>` set_header() function.
+
+.. note:: To IIS users: if you hide the `Server` HTTP header, the "auto"
+ method won't detect IIS, in that case it is advised you explicitly
+ use the "refresh" method.