fix(smtp): proper SMTP dialogue, encoded mails, optional skip-verify

- Explicit SMTP flow (dial -> EHLO -> STARTTLS -> AUTH -> MAIL/RCPT/DATA) with errors naming the refusing step (also logged as smtp_step) - EHLO with the sender's domain instead of "localhost" - Envelope gets the bare address; "Name <addr>" stays in the From header (was rejected as invalid MAIL FROM) - Date and Message-ID headers, RFC 2047 subject, quoted-printable body - SMTP_SKIP_VERIFY / admin switch for self-signed certificates; SMTP checkboxes are switches now - Tests against a fake SMTP server (STARTTLS, 451, display names) Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
2026-10-28 22:28:26 +01:00
1 parent bf0d68e7e1
commit ce321ce579
@@ -0,0 +1,189 @@
+package api
+
+import (
+	"bytes"
+	"crypto/rand"
+	"crypto/tls"
+	"encoding/hex"
+	"fmt"
+	"mime"
+	"mime/quotedprintable"
+	"net"
+	"net/mail"
+	"net/smtp"
+	"os"
+	"strings"
+	"time"
+)
+
+// smtpSettings is the effective mail server configuration (admin settings, else environment).
+type smtpSettings struct {
+	Host, Port, User, Pass, From string
+	TLS                          bool // 465: implicit TLS, otherwise STARTTLS (required when set)
+	SkipVerify                   bool // accept self-signed / mismatching certificates
+}
+
+// smtpStepError names the protocol step at which the mail server refused, e.g. "RCPT TO".
+type smtpStepError struct {
+	Step string
+	Err  error
+}
+
+func (e *smtpStepError) Error() string {
+	return fmt.Sprintf("SMTP-Schritt %s fehlgeschlagen: %v", e.Step, e.Err)
+}
+
+func (e *smtpStepError) Unwrap() error { return e.Err }
+
+const smtpTimeout = 30 * time.Second
+
+func (s *Server) smtpSettings() (smtpSettings, error) {
+	cfg := smtpSettings{Port: "587", TLS: true}
+	if sys, _ := s.store.GetSystemSettings(); sys != nil && strings.TrimSpace(sys.SMTPHost) != "" {
+		cfg = smtpSettings{
+			Host: strings.TrimSpace(sys.SMTPHost), Port: strings.TrimSpace(sys.SMTPPort),
+			User: strings.TrimSpace(sys.SMTPUser), Pass: sys.SMTPPass, From: strings.TrimSpace(sys.SMTPFrom),
+			TLS: sys.SMTPTLS, SkipVerify: sys.SMTPSkipVerify,
+		}
+	} else if strings.TrimSpace(s.cfg.SMTPHost) != "" {
+		cfg = smtpSettings{
+			Host: strings.TrimSpace(s.cfg.SMTPHost), Port: strings.TrimSpace(s.cfg.SMTPPort),
+			User: strings.TrimSpace(s.cfg.SMTPUser), Pass: s.cfg.SMTPPass, From: strings.TrimSpace(s.cfg.SMTPFrom),
+			TLS: s.cfg.SMTPTLS, SkipVerify: s.cfg.SMTPSkipVerify,
+		}
+	}
+	if cfg.Host == "" {
+		return cfg, fmt.Errorf("kein SMTP-Server konfiguriert (bitte in den Administratoreinstellungen oder per Docker-Env hinterlegen)")
+	}
+	if cfg.Port == "" {
+		cfg.Port = "587"
+	}
+	if cfg.From == "" {
+		if strings.Contains(cfg.User, "@") {
+			cfg.From = cfg.User
+		} else {
+			cfg.From = "noreply@mindsift.local"
+		}
+	}
+	return cfg, nil
+}
+
+// ehloName is how MindSift introduces itself (EHLO). It must name the sending side, never "localhost",
+// which strict servers (Exchange/O365, Postfix with HELO checks) refuse: the sender's mail domain,
+// else the machine's hostname.
+func ehloName(from string) string {
+	if at := strings.LastIndex(from, "@"); at >= 0 {
+		if domain := strings.Trim(from[at+1:], " >"); strings.Contains(domain, ".") {
+			return domain
+		}
+	}
+	if h, err := os.Hostname(); err == nil && strings.Contains(h, ".") {
+		return h
+	}
+	return "mindsift.local"
+}
+
+// splitAddress turns "MindSift <alarm@firma.de>" into the bare address for the SMTP envelope
+// (MAIL FROM / RCPT TO only accept that) and the header form with an encoded display name.
+func splitAddress(raw string) (envelope, header string, err error) {
+	addr, err := mail.ParseAddress(strings.TrimSpace(raw))
+	if err != nil {
+		return "", "", fmt.Errorf("ungültige E-Mail-Adresse %q", raw)
+	}
+	return addr.Address, addr.String(), nil
+}
+
+// buildMessage creates an RFC 5322 message: Date and Message-ID headers, RFC 2047 encoded subject
+// (umlauts, emoji) and a quoted-printable UTF-8 body with CRLF line endings.
+func buildMessage(from, to, subject, body string, now time.Time) []byte {
+	idBytes := make([]byte, 12)
+	_, _ = rand.Read(idBytes)
+	domain := ehloName(from)
+
+	var buf bytes.Buffer
+	fmt.Fprintf(&buf, "From: %s\r\n", from)
+	fmt.Fprintf(&buf, "To: %s\r\n", to)
+	fmt.Fprintf(&buf, "Subject: %s\r\n", mime.QEncoding.Encode("utf-8", subject))
+	fmt.Fprintf(&buf, "Date: %s\r\n", now.Format(time.RFC1123Z))
+	fmt.Fprintf(&buf, "Message-ID: <%s@%s>\r\n", hex.EncodeToString(idBytes), domain)
+	buf.WriteString("MIME-Version: 1.0\r\n")
+	buf.WriteString("Content-Type: text/plain; charset=\"utf-8\"\r\n")
+	buf.WriteString("Content-Transfer-Encoding: quoted-printable\r\n\r\n")
+	qp := quotedprintable.NewWriter(&buf)
+	_, _ = qp.Write([]byte(strings.ReplaceAll(strings.ReplaceAll(body, "\r\n", "\n"), "\n", "\r\n")))
+	_ = qp.Close()
+	buf.WriteString("\r\n")
+	return buf.Bytes()
+}
+
+// sendMail runs the SMTP dialogue step by step instead of smtp.SendMail, so it can introduce itself
+// properly, honour SkipVerify and report the exact step a server refuses.
+func sendMail(cfg smtpSettings, to, subject, body string) error {
+	fromAddr, fromHeader, err := splitAddress(cfg.From)
+	if err != nil {
+		return &smtpStepError{"Absender", err}
+	}
+	toAddr, toHeader, err := splitAddress(to)
+	if err != nil {
+		return &smtpStepError{"Empfänger", err}
+	}
+	addr := net.JoinHostPort(cfg.Host, cfg.Port)
+	tlsCfg := &tls.Config{ServerName: cfg.Host, InsecureSkipVerify: cfg.SkipVerify} //nolint:gosec // admin opt-in for self-signed certificates
+	dialer := &net.Dialer{Timeout: smtpTimeout}
+	implicitTLS := cfg.Port == "465" && cfg.TLS
+
+	var conn net.Conn
+	if implicitTLS {
+		conn, err = tls.DialWithDialer(dialer, "tcp", addr, tlsCfg)
+	} else {
+		conn, err = dialer.Dial("tcp", addr)
+	}
+	if err != nil {
+		return &smtpStepError{"Verbindung", err}
+	}
+	_ = conn.SetDeadline(time.Now().Add(2 * smtpTimeout))
+
+	client, err := smtp.NewClient(conn, cfg.Host)
+	if err != nil {
+		_ = conn.Close()
+		return &smtpStepError{"Begrüßung", err}
+	}
+	defer client.Close()
+
+	if err := client.Hello(ehloName(cfg.From)); err != nil {
+		return &smtpStepError{"EHLO", err}
+	}
+	if cfg.TLS && !implicitTLS {
+		if ok, _ := client.Extension("STARTTLS"); !ok {
+			return &smtpStepError{"STARTTLS", fmt.Errorf("der Server bietet kein STARTTLS an (TLS deaktivieren oder Port 465 nutzen)")}
+		}
+		if err := client.StartTLS(tlsCfg); err != nil {
+			return &smtpStepError{"STARTTLS", err}
+		}
+	}
+	if cfg.User != "" || cfg.Pass != "" {
+		if err := client.Auth(smtp.PlainAuth("", cfg.User, cfg.Pass, cfg.Host)); err != nil {
+			return &smtpStepError{"AUTH", err}
+		}
+	}
+	if err := client.Mail(fromAddr); err != nil {
+		return &smtpStepError{"MAIL FROM", err}
+	}
+	if err := client.Rcpt(toAddr); err != nil {
+		return &smtpStepError{"RCPT TO", err}
+	}
+	wc, err := client.Data()
+	if err != nil {
+		return &smtpStepError{"DATA", err}
+	}
+	if _, err := wc.Write(buildMessage(fromHeader, toHeader, subject, body, time.Now())); err != nil {
+		_ = wc.Close()
+		return &smtpStepError{"DATA", err}
+	}
+	if err := wc.Close(); err != nil {
+		// The server answers after the final "." – content filters reject here
+		return &smtpStepError{"Nachricht annehmen", err}
+	}
+	_ = client.Quit()
+	return nil
+}