Feature: Optionally propagate SMTP errors (#588)

* forward smtp errors

* lint and formatting

* forward smtp errors in forward-impl

internal/smtpd/forward.go

@@ -7,23 +7,29 @@ import (
 	"os"
 	"strings"
 
+	"github.com/pkg/errors"
+
 	"github.com/axllent/mailpit/config"
 	"github.com/axllent/mailpit/internal/logger"
 	"github.com/axllent/mailpit/internal/tools"
 )
 
 // Wrapper to forward messages if configured
-func autoForwardMessage(from string, data *[]byte) {
+func autoForwardMessage(from string, data *[]byte) error {
 	if config.SMTPForwardConfig.Host == "" {
-		return
+		return nil
 	}
 
 	if err := forward(from, *data); err != nil {
-		logger.Log().Errorf("[forward] error: %s", err.Error())
-	} else {
-		logger.Log().Debugf("[forward] message from %s to %s via %s:%d",
-			from, config.SMTPForwardConfig.To, config.SMTPForwardConfig.Host, config.SMTPForwardConfig.Port)
+		return errors.WithMessage(err, "[forward] error: %s")
 	}
+
+	logger.Log().Debugf(
+		"[forward] message from %s to %s via %s:%d",
+		from, config.SMTPForwardConfig.To, config.SMTPForwardConfig.Host, config.SMTPForwardConfig.Port,
+	)
+
+	return nil
 }
 
 func createForwardingSMTPClient(config config.SMTPForwardConfigStruct, addr string) (*smtp.Client, error) {
@@ -108,6 +114,9 @@ func forward(from string, msg []byte) error {
 	for _, addr := range to {
 		if err = c.Rcpt(addr); err != nil {
 			logger.Log().Warnf("error response to RCPT command for %s: %s", addr, err.Error())
+			if config.SMTPForwardConfig.ForwardSMTPErrors {
+				return errors.WithMessagef(err, "error response to RCPT command for %s", addr)
+			}
 		}
 	}
 

internal/smtpd/main.go

@@ -9,6 +9,9 @@ import (
 	"regexp"
 	"strings"
 
+	"github.com/lithammer/shortuuid/v4"
+	"github.com/pkg/errors"
+
 	"github.com/axllent/mailpit/config"
 	"github.com/axllent/mailpit/internal/auth"
 	"github.com/axllent/mailpit/internal/logger"
@@ -16,7 +19,6 @@ import (
 	"github.com/axllent/mailpit/internal/storage"
 	"github.com/axllent/mailpit/internal/tools"
 	"github.com/axllent/mailpit/server/websockets"
-	"github.com/lithammer/shortuuid/v4"
 )
 
 var (
@@ -73,10 +75,36 @@ func SaveToDatabase(origin net.Addr, from string, to []string, data []byte, smtp
 	}
 
 	// if enabled, this may conditionally relay the email through to the preconfigured smtp server
-	autoRelayMessage(from, to, &data)
+	if relayErr := autoRelayMessage(from, to, &data); relayErr != nil {
+		logger.Log().Errorf("%s", relayErr.Error())
+
+		if config.SMTPRelayConfig.ForwardSMTPErrors {
+			for {
+				unwrappedErr := errors.Unwrap(relayErr)
+				if unwrappedErr == nil {
+					break
+				}
+				relayErr = unwrappedErr
+			}
+			return "", relayErr
+		}
+	}
 
 	// if enabled, this will forward a copy to preconfigured addresses
-	autoForwardMessage(from, &data)
+	if forwardErr := autoForwardMessage(from, &data); forwardErr != nil {
+		logger.Log().Errorf("%s", forwardErr.Error())
+
+		if config.SMTPForwardConfig.ForwardSMTPErrors {
+			for {
+				unwrappedErr := errors.Unwrap(forwardErr)
+				if unwrappedErr == nil {
+					break
+				}
+				forwardErr = unwrappedErr
+			}
+			return "", forwardErr
+		}
+	}
 
 	// build array of all addresses in the header to compare to the []to array
 	emails, hasBccHeader := scanAddressesInHeader(msg.Header)
@@ -225,15 +253,27 @@ func listenAndServe(addr string, handler MsgIDHandler, authHandler AuthHandler)
 	}
 
 	if config.SMTPAuthAllowInsecure {
-		srv.AuthMechs = map[string]bool{"CRAM-MD5": false, "PLAIN": true, "LOGIN": true}
+		srv.AuthMechs = map[string]bool{
+			"CRAM-MD5": false,
+			"PLAIN":    true,
+			"LOGIN":    true,
+		}
 	}
 
 	if auth.SMTPCredentials != nil {
-		srv.AuthMechs = map[string]bool{"CRAM-MD5": false, "PLAIN": true, "LOGIN": true}
+		srv.AuthMechs = map[string]bool{
+			"CRAM-MD5": false,
+			"PLAIN":    true,
+			"LOGIN":    true,
+		}
 		srv.AuthHandler = authHandler
 		srv.AuthRequired = true
 	} else if config.SMTPAuthAcceptAny {
-		srv.AuthMechs = map[string]bool{"CRAM-MD5": false, "PLAIN": true, "LOGIN": true}
+		srv.AuthMechs = map[string]bool{
+			"CRAM-MD5": false,
+			"PLAIN":    true,
+			"LOGIN":    true,
+		}
 		srv.AuthHandler = authHandlerAny
 	}
 

internal/smtpd/relay.go

@@ -2,19 +2,20 @@ package smtpd
 
 import (
 	"crypto/tls"
-	"errors"
 	"fmt"
 	"net/smtp"
 	"os"
 	"strings"
 
+	"github.com/pkg/errors"
+
 	"github.com/axllent/mailpit/config"
 	"github.com/axllent/mailpit/internal/logger"
 	"github.com/axllent/mailpit/internal/tools"
 )
 
 // Wrapper to auto relay messages if configured
-func autoRelayMessage(from string, to []string, data *[]byte) {
+func autoRelayMessage(from string, to []string, data *[]byte) error {
 	if config.SMTPRelayConfig.BlockedRecipientsRegexp != nil {
 		filteredTo := []string{}
 		for _, address := range to {
@@ -29,15 +30,17 @@ func autoRelayMessage(from string, to []string, data *[]byte) {
 	}
 
 	if len(to) == 0 {
-		return
+		return nil
 	}
 
 	if config.SMTPRelayAll {
 		if err := Relay(from, to, *data); err != nil {
-			logger.Log().Errorf("[relay] error: %s", err.Error())
+			return errors.WithMessage(err, "[relay] error")
 		} else {
-			logger.Log().Debugf("[relay] sent message to %s from %s via %s:%d",
-				strings.Join(to, ", "), from, config.SMTPRelayConfig.Host, config.SMTPRelayConfig.Port)
+			logger.Log().Debugf(
+				"[relay] sent message to %s from %s via %s:%d",
+				strings.Join(to, ", "), from, config.SMTPRelayConfig.Host, config.SMTPRelayConfig.Port,
+			)
 		}
 	} else if config.SMTPRelayMatchingRegexp != nil {
 		filtered := []string{}
@@ -48,16 +51,20 @@ func autoRelayMessage(from string, to []string, data *[]byte) {
 		}
 
 		if len(filtered) == 0 {
-			return
+			return nil
 		}
 
 		if err := Relay(from, filtered, *data); err != nil {
-			logger.Log().Errorf("[relay] error: %s", err.Error())
+			return errors.WithMessage(err, "[relay] error")
 		} else {
-			logger.Log().Debugf("[relay] auto-relay message to %s from %s via %s:%d",
-				strings.Join(filtered, ", "), from, config.SMTPRelayConfig.Host, config.SMTPRelayConfig.Port)
+			logger.Log().Debugf(
+				"[relay] auto-relay message to %s from %s via %s:%d",
+				strings.Join(filtered, ", "), from, config.SMTPRelayConfig.Host, config.SMTPRelayConfig.Port,
+			)
 		}
 	}
+
+	return nil
 }
 
 func createRelaySMTPClient(config config.SMTPRelayConfigStruct, addr string) (*smtp.Client, error) {
@@ -134,26 +141,29 @@ func Relay(from string, to []string, msg []byte) error {
 	}
 
 	if err = c.Mail(from); err != nil {
-		return fmt.Errorf("error response to MAIL command: %s", err.Error())
+		return errors.WithMessage(err, "error sending MAIL command")
 	}
 
 	for _, addr := range to {
 		if err = c.Rcpt(addr); err != nil {
 			logger.Log().Warnf("error response to RCPT command for %s: %s", addr, err.Error())
+			if config.SMTPRelayConfig.ForwardSMTPErrors {
+				return errors.WithMessagef(err, "error response to RCPT command for %s", addr)
+			}
 		}
 	}
 
 	w, err := c.Data()
 	if err != nil {
-		return fmt.Errorf("error response to DATA command: %s", err.Error())
+		return errors.WithMessage(err, "error response to DATA command")
 	}
 
 	if _, err := w.Write(msg); err != nil {
-		return fmt.Errorf("error sending message: %s", err.Error())
+		return errors.WithMessage(err, "error sending message")
 	}
 
 	if err := w.Close(); err != nil {
-		return fmt.Errorf("error closing connection: %s", err.Error())
+		return errors.WithMessage(err, "error closing connection")
 	}
 
 	return c.Quit()
@@ -186,7 +196,10 @@ type loginAuth struct {
 
 // LoginAuth authentication
 func LoginAuth(username, password string) smtp.Auth {
-	return &loginAuth{username, password}
+	return &loginAuth{
+		username,
+		password,
+	}
 }
 
 func (a *loginAuth) Start(_ *smtp.ServerInfo) (string, []byte, error) {