Allow smtpd to work as a backup MX, relaying only to MXs with higher

priority in the DNS record. For example:

   accept for domain "foo.org" relay backup "mx3.foo.org"

will relay mails for "foo.org" using only hosts with higher priority
(i.e. lower value) than "mx3.foo.org", which is supposed to be the
current server.

If the specified backup MX is not found in the DNS record, relaying
works as normal.

ok gilles@

1 files changed, 7 insertions, 3 deletions

diff --git a/usr.sbin/smtpd/smtpd.h b/usr.sbin/smtpd/smtpd.h
index a30c5269b1f..0bcc8edc7f5 100644
--- a/usr.sbin/smtpd/smtpd.h
+++ b/usr.sbin/smtpd/smtpd.h
@@ -1,4 +1,4 @@
-/*	$OpenBSD: smtpd.h,v 1.328 2012/08/21 13:13:17 eric Exp $	*/
+/*	$OpenBSD: smtpd.h,v 1.329 2012/08/21 20:19:46 eric Exp $	*/
 
 /*
  * Copyright (c) 2008 Gilles Chehade <gilles@openbsd.org>
@@ -79,6 +79,8 @@
 #define F_AUTH			 0x04
 #define F_SSL			(F_SMTPS|F_STARTTLS)
 
+#define	F_BACKUP		0x10	/* XXX */
+
 #define F_SCERT			0x01
 #define F_CCERT			0x02
 
@@ -88,6 +90,7 @@
 #define ROUTE_SSL		(ROUTE_STARTTLS | ROUTE_SMTPS)
 #define ROUTE_AUTH		0x04
 #define ROUTE_MX		0x08
+#define ROUTE_BACKUP		0x10	/* XXX */
 
 typedef uint32_t	objid_t;
 
@@ -653,12 +656,12 @@ enum dns_status {
 struct dns {
 	uint64_t		 id;
 	char			 host[MAXHOSTNAMELEN];
+	char			 backup[MAXHOSTNAMELEN];
 	int			 port;
 	int			 error;
 	int			 type;
 	struct imsgev		*asker;
 	struct sockaddr_storage	 ss;
-	struct dns		*next;
 };
 
 struct secret {
@@ -733,6 +736,7 @@ struct mta_route {
 
 	uint8_t			 flags;
 	char			*hostname;
+	char			*backupname;
 	uint16_t		 port;
 	char			*cert;
 	char			*auth;
@@ -954,7 +958,7 @@ struct delivery_backend *delivery_backend_lookup(enum action_type);
 
 /* dns.c */
 void dns_query_host(char *, int, uint64_t);
-void dns_query_mx(char *, int, uint64_t);
+void dns_query_mx(char *, char *, int, uint64_t);
 void dns_query_ptr(struct sockaddr_storage *, uint64_t);
 void dns_async(struct imsgev *, int, struct dns *);