diff --git a/debian/patches/36_check_smtp_adding_proxy_header b/debian/patches/36_check_smtp_adding_proxy_header
new file mode 100644
index 0000000..aeb6b86
--- /dev/null
+++ b/debian/patches/36_check_smtp_adding_proxy_header
@@ -0,0 +1,129 @@
+From ce85affd208cd8c873dd88c17b8d3d0540c8872e Mon Sep 17 00:00:00 2001
+From: Patrick Uiterwijk <patrick@puiterwijk.org>
+Date: Thu, 13 Dec 2018 18:24:53 +0100
+Subject: [PATCH 1/5] check_smtp: Add option to prefix PROXY header
+
+This enables checks of SMTP servers that expect the haproxy
+PROXY protocol:  -o smtpd_upstream_proxy_protocol=haproxy.
+
+Backported from nagios-plugins:
+https://github.com/nagios-plugins/nagios-plugins/commit/3246efe923b5482c5024c40e593ce942e628a3cb
+---
+ plugins/check_smtp.c | 17 ++++++++++++++++-
+ 1 file changed, 16 insertions(+), 1 deletion(-)
+
+diff --git a/plugins/check_smtp.c b/plugins/check_smtp.c
+index eaa7eebab..addabfc66 100644
+--- a/plugins/check_smtp.c
++++ b/plugins/check_smtp.c
+@@ -52,6 +52,7 @@ int days_till_exp_warn, days_till_exp_crit;
+ enum {
+ 	SMTP_PORT	= 25
+ };
++#define PROXY_PREFIX "PROXY TCP4 0.0.0.0 0.0.0.0 25 25\r\n"
+ #define SMTP_EXPECT "220"
+ #define SMTP_HELO "HELO "
+ #define SMTP_EHLO "EHLO "
+@@ -102,6 +103,7 @@ double critical_time = 0;
+ int check_critical_time = FALSE;
+ int verbose = 0;
+ int use_ssl = FALSE;
++short use_proxy_prefix = FALSE;
+ short use_ehlo = FALSE;
+ short use_lhlo = FALSE;
+ short ssl_established = 0;
+@@ -184,6 +186,13 @@ main (int argc, char **argv)
+ 
+ 	if (result == STATE_OK) { /* we connected */
+ 
++		/* If requested, send PROXY header */
++		if (use_proxy_prefix) {
++			if (verbose)
++				printf ("Sending header %s\n", PROXY_PREFIX);
++			send(sd, PROXY_PREFIX, strlen(PROXY_PREFIX), 0);
++		}
++
+ 		/* watch for the SMTP connection string and */
+ 		/* return a WARNING status if we couldn't read any data */
+ 		if (recvlines(buffer, MAX_INPUT_BUFFER) <= 0) {
+@@ -478,6 +487,7 @@ process_arguments (int argc, char **argv)
+ 		{"starttls",no_argument,0,'S'},
+ 		{"certificate",required_argument,0,'D'},
+ 		{"ignore-quit-failure",no_argument,0,'q'},
++		{"proxy",no_argument,0,'r'},
+ 		{0, 0, 0, 0}
+ 	};
+ 
+@@ -494,7 +504,7 @@ process_arguments (int argc, char **argv)
+ 	}
+ 
+ 	while (1) {
+-		c = getopt_long (argc, argv, "+hVv46Lt:p:f:e:c:w:H:C:R:SD:F:A:U:P:q",
++		c = getopt_long (argc, argv, "+hVv46Lrt:p:f:e:c:w:H:C:R:SD:F:A:U:P:q",
+ 		                 longopts, &option);
+ 
+ 		if (c == -1 || c == EOF)
+@@ -621,6 +631,9 @@ process_arguments (int argc, char **argv)
+ 			use_ssl = TRUE;
+ 			use_ehlo = TRUE;
+ 			break;
++		case 'r':
++			use_proxy_prefix = TRUE;
++			break;
+ 		case 'L':
+ 			use_lhlo = TRUE;
+ 			break;
+@@ -819,6 +832,8 @@ print_help (void)
+   printf ("    %s\n", _("FROM-address to include in MAIL command, required by Exchange 2000")),
+   printf (" %s\n", "-F, --fqdn=STRING");
+   printf ("    %s\n", _("FQDN used for HELO"));
++  printf (" %s\n", "-r, --proxy");
++  printf ("    %s\n", _("Use PROXY protocol prefix for the connection."));
+ #ifdef HAVE_SSL
+   printf (" %s\n", "-D, --certificate=INTEGER[,INTEGER]");
+   printf ("    %s\n", _("Minimum number of days a certificate has to be valid."));
+
+From 6d5e81fcbadbef557cf3f61ce7fd6ef73e25683e Mon Sep 17 00:00:00 2001
+From: Franz Schwartau <franz@electromail.org>
+Date: Mon, 12 Jun 2023 15:55:32 +0200
+Subject: [PATCH 2/5] check_smtp: add missing -r option in usage
+
+---
+ plugins/check_smtp.c | 2 +-
+ 1 file changed, 1 insertion(+), 1 deletion(-)
+
+diff --git a/plugins/check_smtp.c b/plugins/check_smtp.c
+index addabfc66..a1debd25f 100644
+--- a/plugins/check_smtp.c
++++ b/plugins/check_smtp.c
+@@ -875,6 +875,6 @@ print_usage (void)
+   printf ("%s\n", _("Usage:"));
+   printf ("%s -H host [-p port] [-4|-6] [-e expect] [-C command] [-R response] [-f from addr]\n", progname);
+   printf ("[-A authtype -U authuser -P authpass] [-w warn] [-c crit] [-t timeout] [-q]\n");
+-  printf ("[-F fqdn] [-S] [-L] [-D warn days cert expire[,crit days cert expire]] [-v] \n");
++  printf ("[-F fqdn] [-S] [-L] [-D warn days cert expire[,crit days cert expire]] [-r] [-v] \n");
+ }
+ 
+
+From d762fb137401491270c898febe07e34ba200e388 Mon Sep 17 00:00:00 2001
+From: Franz Schwartau <franz@electromail.org>
+Date: Mon, 12 Jun 2023 22:09:54 +0200
+Subject: [PATCH 5/5] check_smtp: update year in copyright header
+
+---
+ plugins/check_smtp.c | 2 +-
+ 1 file changed, 1 insertion(+), 1 deletion(-)
+
+diff --git a/plugins/check_smtp.c b/plugins/check_smtp.c
+index a1debd25f..70191ad92 100644
+--- a/plugins/check_smtp.c
++++ b/plugins/check_smtp.c
+@@ -3,7 +3,7 @@
+ * Monitoring check_smtp plugin
+ * 
+ * License: GPL
+-* Copyright (c) 2000-2007 Monitoring Plugins Development Team
++* Copyright (c) 2000-2023 Monitoring Plugins Development Team
+ * 
+ * Description:
+ * 
diff --git a/debian/patches/series b/debian/patches/series
index a9c0d8b..e0639fc 100644
--- a/debian/patches/series
+++ b/debian/patches/series
@@ -22,3 +22,4 @@
 32_check_disk_add_ignore_missing
 33_check_procs_exclude-process
 34_check_curl_fix_compare_warning
+36_check_smtp_adding_proxy_header