From d8860fc91779819aca3ce77683d68e7bcd18309a Mon Sep 17 00:00:00 2001
From: Ben Ubois <ben@benubois.com>
Date: Fri, 7 May 2021 14:08:10 -0700
Subject: [PATCH 1/2] Added external command support.

---
 config.go     |  5 +++--
 main.go       | 28 +++++++++++++++++++++++++++-
 smtprelay.ini |  3 +++
 3 files changed, 33 insertions(+), 3 deletions(-)

diff --git a/config.go b/config.go
index 40bf13d..3d32766 100644
--- a/config.go
+++ b/config.go
@@ -34,6 +34,7 @@ var (
 	allowedRecipStr   = flag.String("allowed_recipients", "", "Regular expression for valid TO EMail addresses")
 	allowedRecipients *regexp.Regexp
 	allowedUsers      = flag.String("allowed_users", "", "Path to file with valid users/passwords")
+	command           = flag.String("command", "", "Path to pipe command")
 	remoteHost        = flag.String("remote_host", "", "Outgoing SMTP server")
 	remoteUser        = flag.String("remote_user", "", "Username for authentication on outgoing SMTP server")
 	remotePass        = flag.String("remote_pass", "", "Password for authentication on outgoing SMTP server")
@@ -172,8 +173,8 @@ func ConfigLoad() {
 	// Set up logging as soon as possible
 	setupLogger()
 
-	if *remoteHost == "" {
-		log.Warn("remote_host not set; mail will not be forwarded!")
+	if *remoteHost == "" && *command == "" {
+		log.Warn("no remote_host or command set; mail will not be forwarded!")
 	}
 
 	setupAllowedNetworks()
diff --git a/main.go b/main.go
index 8e239eb..185a977 100644
--- a/main.go
+++ b/main.go
@@ -1,11 +1,13 @@
 package main
 
 import (
+	"bytes"
 	"crypto/tls"
 	"fmt"
 	"net"
 	"net/textproto"
 	"os"
+	"os/exec"
 	"os/signal"
 	"strings"
 	"syscall"
@@ -163,8 +165,32 @@ func mailHandler(peer smtpd.Peer, env smtpd.Envelope) error {
 		"uuid": generateUUID(),
 	})
 
+	if *remoteHost == "" && *command == "" {
+		logger.Warning("no remote_host or command set; discarding mail")
+		return nil
+	}
+
+	if *command != "" {
+		cmdLogger := logger.WithField("command", *command)
+
+		var stdout bytes.Buffer
+		var stderr bytes.Buffer
+
+		cmd := exec.Command(*command)
+		cmd.Stdin = bytes.NewReader(env.Data)
+		cmd.Stdout = &stdout
+		cmd.Stderr = &stderr
+
+		err := cmd.Run()
+		if err != nil {
+			cmdLogger.WithError(err).Error(stderr.String())
+			return nil
+		}
+
+		cmdLogger.Info("pipe command successful: " + stdout.String())
+	}
+
 	if *remoteHost == "" {
-		logger.Warning("remote_host not set; discarding mail")
 		return nil
 	}
 
diff --git a/smtprelay.ini b/smtprelay.ini
index b47f103..5fb682b 100644
--- a/smtprelay.ini
+++ b/smtprelay.ini
@@ -78,3 +78,6 @@
 
 ; Sender e-mail address on outgoing SMTP server
 ;remote_sender = 
+
+; Pipe messages to external command
+;command = /usr/local/bin/script
\ No newline at end of file

From 3f627d3281e2b6e4313222d07b55758e4bfdadc1 Mon Sep 17 00:00:00 2001
From: Ben Ubois <ben@benubois.com>
Date: Sat, 8 May 2021 11:56:28 -0700
Subject: [PATCH 2/2] Move AddReceivedLine before further processing.

---
 main.go | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/main.go b/main.go
index 185a977..d83493c 100644
--- a/main.go
+++ b/main.go
@@ -170,6 +170,8 @@ func mailHandler(peer smtpd.Peer, env smtpd.Envelope) error {
 		return nil
 	}
 
+	env.AddReceivedLine(peer)
+
 	if *command != "" {
 		cmdLogger := logger.WithField("command", *command)
 
@@ -196,8 +198,6 @@ func mailHandler(peer smtpd.Peer, env smtpd.Envelope) error {
 
 	logger.Info("delivering mail from peer using smarthost")
 
-	env.AddReceivedLine(peer)
-
 	var sender string
 
 	if *remoteSender == "" {