Chore: Allow sendmail to send to untrusted TLS server

sendmail/cmd/smtp.go

@@ -2,11 +2,15 @@
 package cmd
 
 import (
+	"crypto/tls"
+	"errors"
 	"fmt"
 	"net"
 	"net/mail"
 	"net/smtp"
+	"net/url"
 	"os"
+	"strings"
 
 	"github.com/axllent/mailpit/internal/logger"
 )
@@ -27,7 +31,7 @@ func Send(addr string, from string, to []string, msg []byte) error {
 	}
 
 	if !isSocket {
-		return smtp.SendMail(addr, nil, fromAddress.Address, to, msg)
+		return sendMail(addr, nil, fromAddress.Address, to, msg)
 	}
 
 	conn, err := net.Dial("unix", socketPath)
@@ -69,3 +73,82 @@ func Send(addr string, from string, to []string, msg []byte) error {
 
 	return nil
 }
+
+func sendMail(addr string, a smtp.Auth, from string, to []string, msg []byte) error {
+	addrParsed, err := url.Parse(addr) // ensure addr is a valid URL
+	if err != nil {
+		return fmt.Errorf("invalid address: %s", addr)
+	}
+
+	host := addrParsed.Host
+	if err := validateLine(from); err != nil {
+		return err
+	}
+
+	for _, recipient := range to {
+		if err := validateLine(recipient); err != nil {
+			return err
+		}
+	}
+
+	c, err := smtp.Dial(addr)
+	if err != nil {
+		return err
+	}
+	defer func() { _ = c.Close() }()
+
+	if err = c.Hello(addr); err != nil {
+		return err
+	}
+
+	if ok, _ := c.Extension("STARTTLS"); ok {
+		config := &tls.Config{ServerName: host, InsecureSkipVerify: true} // #nosec
+		if err = c.StartTLS(config); err != nil {
+			return err
+		}
+	}
+
+	if a != nil {
+		if ok, _ := c.Extension("AUTH"); !ok {
+			return errors.New("smtp: server doesn't support AUTH")
+		}
+		if err = c.Auth(a); err != nil {
+			return err
+		}
+	}
+
+	if err = c.Mail(from); err != nil {
+		return err
+	}
+
+	for _, addr := range to {
+		if err = c.Rcpt(addr); err != nil {
+			return err
+		}
+	}
+
+	w, err := c.Data()
+	if err != nil {
+		return err
+	}
+
+	_, err = w.Write(msg)
+	if err != nil {
+		return err
+	}
+
+	err = w.Close()
+	if err != nil {
+		return err
+	}
+
+	return c.Quit()
+}
+
+// validateLine checks to see if a line has CR or LF as per RFC 5321.
+func validateLine(line string) error {
+	if strings.ContainsAny(line, "\n\r") {
+		return errors.New("smtp: A line must not contain CR or LF")
+	}
+	return nil
+}