believe it or not, mail(1) completely explodes if the From header has the date written in the wrong format

src/etc/root/root.mail

@@ -1,4 +1,4 @@
-From deraadt@do-not-reply.openbsd.org Tue June  1 04:50:00 MDT 1999
+From deraadt@do-not-reply.openbsd.org Tue Jun  1 04:50:00 MDT 1999
 Return-Path: root
 Date: Tue June  1 04:50:00 MDT 1999
 From: deraadt@do-not-reply.openbsd.org (Theo de Raadt)