diff --git a/runtime/indent/mail.vim b/runtime/indent/mail.vim
index 6246b40..22bb0f7 100644
--- a/runtime/indent/mail.vim
+++ b/runtime/indent/mail.vim
@@ -1,7 +1,7 @@
 " Vim indent file
 " Language:	Mail
 " Maintainer:	Bram Moolenaar
-" Last Change:	2009 Jun 03
+" Last Change:	2021 Sep 26
 
 if exists("b:did_indent")
   finish
@@ -11,3 +11,5 @@
 " What works best is auto-indenting, disable other indenting.
 " For formatting see the ftplugin.
 setlocal autoindent nosmartindent nocindent indentexpr=
+
+let b:undo_indent = "setl ai< cin< inde< si<"