feat: try StartTLS if SMTP server doesn't support pure TLS (#1676)

* feat: try starttls if smtp server doesn't support pure tls

* chore: fix log id

* fix: errors.As is not working with own error type

internal/notification/providers/email/provider.go

@@ -2,11 +2,13 @@ package email
 
 import (
 	"crypto/tls"
+	"net"
+	"net/smtp"
+
 	"github.com/caos/logging"
 	caos_errs "github.com/caos/zitadel/internal/errors"
 	"github.com/caos/zitadel/internal/notification/providers"
-	"net"
-	"net/smtp"
+	"github.com/pkg/errors"
 )
 
 type Email struct {
@@ -93,31 +95,51 @@ func (smtpConfig SMTP) connectToSMTP(tlsRequired bool) (client *smtp.Client, err
 func (smtpConfig SMTP) getSMPTClient() (*smtp.Client, error) {
 	client, err := smtp.Dial(smtpConfig.Host)
 	if err != nil {
-		return nil, caos_errs.ThrowInternal(err, "EMAIL-skwos", "Could not make smtp dial")
+		return nil, caos_errs.ThrowInternal(err, "EMAIL-skwos", "could not make smtp dial")
 	}
 	return client, nil
 }
 
 func (smtpConfig SMTP) getSMPTClientWithTls(host string) (*smtp.Client, error) {
 	conn, err := tls.Dial("tcp", smtpConfig.Host, &tls.Config{})
+
+	if errors.As(err, &tls.RecordHeaderError{}) {
+		logging.Log("MAIN-xKIzT").OnError(err).Warn("could not connect using normal tls. trying starttls instead...")
+		return smtpConfig.getSMPTClientWithStartTls(host)
+	}
+
 	if err != nil {
-		return nil, caos_errs.ThrowInternal(err, "EMAIL-sl39s", "Could not make tls dial")
+		return nil, caos_errs.ThrowInternal(err, "EMAIL-sl39s", "could not make tls dial")
 	}
 
 	client, err := smtp.NewClient(conn, host)
 	if err != nil {
-		return nil, caos_errs.ThrowInternal(err, "EMAIL-skwi4", "Could not create smtp client")
+		return nil, caos_errs.ThrowInternal(err, "EMAIL-skwi4", "could not create smtp client")
 	}
 	return client, err
 }
 
+func (smtpConfig SMTP) getSMPTClientWithStartTls(host string) (*smtp.Client, error) {
+	client, err := smtpConfig.getSMPTClient()
+	if err != nil {
+		return nil, err
+	}
+
+	if err := client.StartTLS(&tls.Config{
+		ServerName: host,
+	}); err != nil {
+		return nil, caos_errs.ThrowInternal(err, "EMAIL-guvsQ", "could not start tls")
+	}
+	return client, nil
+}
+
 func (smtpConfig SMTP) smtpAuth(client *smtp.Client, host string) error {
 	if !smtpConfig.HasAuth() {
 		return nil
 	}
 	// Auth
 	auth := smtp.PlainAuth("", smtpConfig.User, smtpConfig.Password, host)
 	err := client.Auth(auth)
-	logging.Log("EMAIL-s9kfs").WithField("smtp user", smtpConfig.User).OnError(err).Debug("Could not add smtp auth")
+	logging.Log("EMAIL-s9kfs").WithField("smtp user", smtpConfig.User).OnError(err).Debug("could not add smtp auth")
 	return err
 }