diff -up evolution-ews-3.18.5/src/addressbook/e-book-backend-ews.c.ntlm-auth-test-failure evolution-ews-3.18.5/src/addressbook/e-book-backend-ews.c
--- evolution-ews-3.18.5/src/addressbook/e-book-backend-ews.c.ntlm-auth-test-failure	2015-09-21 11:59:31.000000000 +0200
+++ evolution-ews-3.18.5/src/addressbook/e-book-backend-ews.c	2016-04-20 22:54:21.031556789 +0200
@@ -4170,6 +4170,13 @@ e_book_backend_ews_authenticate_sync (EB
 	} else {
 		ews_backend->priv->is_writable = FALSE;
 		e_backend_set_online (backend, FALSE);
+
+		if (e_ews_connection_utils_get_without_password (ews_settings) &&
+			   result == E_SOURCE_AUTHENTICATION_REJECTED &&
+			   !e_named_parameters_exists (credentials, E_SOURCE_CREDENTIAL_PASSWORD)) {
+			e_ews_connection_utils_force_off_ntlm_auth_check ();
+			result = E_SOURCE_AUTHENTICATION_REQUIRED;
+		}
 	}
 
 	e_book_backend_set_writable (E_BOOK_BACKEND (backend), ews_backend->priv->is_writable);
diff -up evolution-ews-3.18.5/src/calendar/e-cal-backend-ews.c.ntlm-auth-test-failure evolution-ews-3.18.5/src/calendar/e-cal-backend-ews.c
--- evolution-ews-3.18.5/src/calendar/e-cal-backend-ews.c.ntlm-auth-test-failure	2015-09-21 11:59:31.000000000 +0200
+++ evolution-ews-3.18.5/src/calendar/e-cal-backend-ews.c	2016-04-20 22:54:21.032556789 +0200
@@ -4341,6 +4341,11 @@ e_cal_backend_ews_authenticate_sync (EBa
 
 		ews_start_sync (cal_backend);
 		cbews_listen_notifications_cb (cal_backend, NULL, ews_settings);
+	} else if (e_ews_connection_utils_get_without_password (ews_settings) &&
+		   result == E_SOURCE_AUTHENTICATION_REJECTED &&
+		   !e_named_parameters_exists (credentials, E_SOURCE_CREDENTIAL_PASSWORD)) {
+		e_ews_connection_utils_force_off_ntlm_auth_check ();
+		result = E_SOURCE_AUTHENTICATION_REQUIRED;
 	}
 
 	g_object_unref (connection);
diff -up evolution-ews-3.18.5/src/collection/e-ews-backend.c.ntlm-auth-test-failure evolution-ews-3.18.5/src/collection/e-ews-backend.c
--- evolution-ews-3.18.5/src/collection/e-ews-backend.c.ntlm-auth-test-failure	2015-09-21 11:59:31.000000000 +0200
+++ evolution-ews-3.18.5/src/collection/e-ews-backend.c	2016-04-20 22:54:21.032556789 +0200
@@ -1045,6 +1045,11 @@ ews_backend_authenticate_sync (EBackend
 		e_collection_backend_authenticate_children (E_COLLECTION_BACKEND (backend), credentials);
 
 		e_ews_backend_sync_folders (ews_backend, NULL, ews_backend_folders_synced_cb, NULL);
+	} else if (e_ews_connection_utils_get_without_password (ews_settings) &&
+		   result == E_SOURCE_AUTHENTICATION_REJECTED &&
+		   !e_named_parameters_exists (credentials, E_SOURCE_CREDENTIAL_PASSWORD)) {
+		e_ews_connection_utils_force_off_ntlm_auth_check ();
+		result = E_SOURCE_AUTHENTICATION_REQUIRED;
 	}
 
 	return result;
diff -up evolution-ews-3.18.5/src/configuration/e-ews-config-utils.c.ntlm-auth-test-failure evolution-ews-3.18.5/src/configuration/e-ews-config-utils.c
--- evolution-ews-3.18.5/src/configuration/e-ews-config-utils.c.ntlm-auth-test-failure	2015-06-17 18:07:41.000000000 +0200
+++ evolution-ews-3.18.5/src/configuration/e-ews-config-utils.c	2016-04-20 22:54:21.032556789 +0200
@@ -383,12 +383,18 @@ e_ews_config_utils_open_connection_for (
 
 			if (result != E_SOURCE_AUTHENTICATION_ACCEPTED) {
 				g_clear_object (&conn);
-				break;
+				if (result != E_SOURCE_AUTHENTICATION_REJECTED || local_error)
+					break;
 			}
-		} else {
+		}
+
+		if (!conn) {
 			EShell *shell;
 			TryCredentialsData data;
 
+			e_ews_connection_utils_force_off_ntlm_auth_check ();
+			g_clear_error (&local_error);
+
 			shell = e_shell_get_default ();
 
 			data.ews_settings = g_object_ref (ews_settings);
diff -up evolution-ews-3.18.5/src/configuration/e-mail-config-ews-autodiscover.c.ntlm-auth-test-failure evolution-ews-3.18.5/src/configuration/e-mail-config-ews-autodiscover.c
--- evolution-ews-3.18.5/src/configuration/e-mail-config-ews-autodiscover.c.ntlm-auth-test-failure	2015-03-23 08:28:34.000000000 +0100
+++ evolution-ews-3.18.5/src/configuration/e-mail-config-ews-autodiscover.c	2016-04-20 22:54:21.032556789 +0200
@@ -169,13 +169,21 @@ mail_config_ews_autodiscover_run_thread
 	gboolean success = FALSE;
 
 	if (!g_cancellable_set_error_if_cancelled (cancellable, &local_error) && !local_error) {
-		if (e_ews_connection_utils_get_without_password (async_context->ews_settings)) {
+		gboolean without_password;
+
+		without_password = e_ews_connection_utils_get_without_password (async_context->ews_settings);
+		if (without_password) {
 			success = e_ews_autodiscover_ws_url_sync (
 				async_context->ews_settings, async_context->email_address, "",
 				cancellable, &local_error);
-		} else {
+		}
+
+		if (!without_password || g_error_matches (local_error, SOUP_HTTP_ERROR, SOUP_STATUS_UNAUTHORIZED)) {
 			EShell *shell;
 
+			e_ews_connection_utils_force_off_ntlm_auth_check ();
+			g_clear_error (&local_error);
+
 			shell = e_shell_get_default ();
 
 			success = e_credentials_prompter_loop_prompt_sync (e_shell_get_credentials_prompter (shell),
diff -up evolution-ews-3.18.5/src/server/e-ews-connection-utils.c.ntlm-auth-test-failure evolution-ews-3.18.5/src/server/e-ews-connection-utils.c
--- evolution-ews-3.18.5/src/server/e-ews-connection-utils.c.ntlm-auth-test-failure	2014-08-11 09:12:45.000000000 +0200
+++ evolution-ews-3.18.5/src/server/e-ews-connection-utils.c	2016-04-20 22:54:21.032556789 +0200
@@ -67,6 +67,8 @@ e_ews_connection_utils_check_element (co
 	return TRUE;
 }
 
+static gboolean force_off_ntlm_auth_check = FALSE;
+
 static gboolean
 ews_connect_check_ntlm_available (void)
 {
@@ -80,6 +82,9 @@ ews_connect_check_ntlm_available (void)
 	gchar *command;
 	gint ret;
 
+	if (force_off_ntlm_auth_check)
+		return FALSE;
+
 	/* We are attempting to predict what libsoup will do. */
 	helper = g_getenv ("SOUP_NTLM_AUTH_DEBUG");
 	if (!helper)
@@ -145,6 +150,11 @@ ews_connect_check_ntlm_available (void)
 #endif
 }
 
+void
+e_ews_connection_utils_force_off_ntlm_auth_check (void)
+{
+	force_off_ntlm_auth_check = TRUE;
+}
 
 /* Should we bother to attempt a connection without a password? Remember,
  * this is *purely* an optimisation to avoid that extra round-trip if we
diff -up evolution-ews-3.18.5/src/server/e-ews-connection-utils.h.ntlm-auth-test-failure evolution-ews-3.18.5/src/server/e-ews-connection-utils.h
--- evolution-ews-3.18.5/src/server/e-ews-connection-utils.h.ntlm-auth-test-failure	2014-08-11 09:12:45.000000000 +0200
+++ evolution-ews-3.18.5/src/server/e-ews-connection-utils.h	2016-04-20 22:54:21.032556789 +0200
@@ -32,6 +32,8 @@ gboolean	e_ews_connection_utils_check_el
 							 const gchar *element_name,
 							 const gchar *expected_name);
 
+void		e_ews_connection_utils_force_off_ntlm_auth_check
+							(void);
 gboolean	e_ews_connection_utils_get_without_password
 							(CamelEwsSettings *ews_settings);