feat: send test mail (#7968)

# Which Problems Are Solved

- Zitadel doesn't have a way to test SMTP settings either before
creating a new provider or once the SMTP provider has been created.
- Zitadel SMTP messages can be more informative for usual errors

# How the Problems Are Solved

- A new step is added to the new/update SMTP provider wizard that allows
us to test a configuration. The result is shown in a text area.
- From the table of SMTP providers you can test your settings too.
- The email address to send the email is by default the email address
for the logged in user as suggested.
- Some of the SMTP error messages have been changed to give more
information about the possible situation. For example: could not contact
with the SMTP server, check the port, firewall issues... instead of
could not dial

Here's a video showing this new option in action:


https://github.com/zitadel/zitadel/assets/30386061/50128ba1-c9fa-4481-8eec-e79a3ca69bda

# Additional Changes

Replace this example text with a concise list of additional changes that
this PR introduces, that are not directly solving the initial problem
but are related.
For example:
- The docs explicitly describe that the property XY is mandatory
- Adds missing translations for validations.

# Additional Context

- Closes #4504

internal/notification/channels/smtp/channel.go

@@ -41,22 +41,22 @@ func (email *Email) HandleMessage(message channels.Message) error {
 	defer email.smtpClient.Close()
 	emailMsg, ok := message.(*messages.Email)
 	if !ok {
-		return zerrors.ThrowInternal(nil, "EMAIL-s8JLs", "message is not EmailMessage")
+		return zerrors.ThrowInternal(nil, "EMAIL-s8JLs", "Errors.SMTP.NotEmailMessage")
 	}
 
 	if emailMsg.Content == "" || emailMsg.Subject == "" || len(emailMsg.Recipients) == 0 {
-		return zerrors.ThrowInternalf(nil, "EMAIL-zGemZ", "subject, recipients and content must be set but got subject %s, recipients length %d and content length %d", emailMsg.Subject, len(emailMsg.Recipients), len(emailMsg.Content))
+		return zerrors.ThrowInternal(nil, "EMAIL-zGemZ", "Errors.SMTP.RequiredAttributes")
 	}
 	emailMsg.SenderEmail = email.senderAddress
 	emailMsg.SenderName = email.senderName
 	emailMsg.ReplyToAddress = email.replyToAddress
 	// To && From
 	if err := email.smtpClient.Mail(emailMsg.SenderEmail); err != nil {
-		return zerrors.ThrowInternalf(err, "EMAIL-s3is3", "could not set sender: %v", emailMsg.SenderEmail)
+		return zerrors.ThrowInternal(err, "EMAIL-s3is3", "Errors.SMTP.CouldNotSetSender")
 	}
 	for _, recp := range append(append(emailMsg.Recipients, emailMsg.CC...), emailMsg.BCC...) {
 		if err := email.smtpClient.Rcpt(recp); err != nil {
-			return zerrors.ThrowInternalf(err, "EMAIL-s4is4", "could not set recipient: %v", recp)
+			return zerrors.ThrowInternal(err, "EMAIL-s4is4", "Errors.SMTP.CouldNotSetRecipient")
 		}
 	}
 
@@ -87,7 +87,7 @@ func (email *Email) HandleMessage(message channels.Message) error {
 func (smtpConfig SMTP) connectToSMTP(tlsRequired bool) (client *smtp.Client, err error) {
 	host, _, err := net.SplitHostPort(smtpConfig.Host)
 	if err != nil {
-		return nil, zerrors.ThrowInternal(err, "EMAIL-spR56", "could not split host and port for connect to smtp")
+		return nil, zerrors.ThrowInternal(err, "EMAIL-spR56", "Errors.SMTP.CouldNotSplit")
 	}
 
 	if !tlsRequired {
@@ -109,7 +109,7 @@ func (smtpConfig SMTP) connectToSMTP(tlsRequired bool) (client *smtp.Client, err
 func (smtpConfig SMTP) getSMTPClient() (*smtp.Client, error) {
 	client, err := smtp.Dial(smtpConfig.Host)
 	if err != nil {
-		return nil, zerrors.ThrowInternal(err, "EMAIL-skwos", "could not make smtp dial")
+		return nil, zerrors.ThrowInternal(err, "EMAIL-skwos", "Errors.SMTP.CouldNotDial")
 	}
 	return client, nil
 }
@@ -118,17 +118,17 @@ func (smtpConfig SMTP) getSMTPClientWithTls(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...")
+		logging.OnError(err).Warn("could not connect using normal tls. trying starttls instead...")
 		return smtpConfig.getSMTPClientWithStartTls(host)
 	}
 
 	if err != nil {
-		return nil, zerrors.ThrowInternal(err, "EMAIL-sl39s", "could not make tls dial")
+		return nil, zerrors.ThrowInternal(err, "EMAIL-sl39s", "Errors.SMTP.CouldNotDialTLS")
 	}
 
 	client, err := smtp.NewClient(conn, host)
 	if err != nil {
-		return nil, zerrors.ThrowInternal(err, "EMAIL-skwi4", "could not create smtp client")
+		return nil, zerrors.ThrowInternal(err, "EMAIL-skwi4", "Errors.SMTP.CouldNotCreateClient")
 	}
 	return client, err
 }
@@ -142,7 +142,7 @@ func (smtpConfig SMTP) getSMTPClientWithStartTls(host string) (*smtp.Client, err
 	if err := client.StartTLS(&tls.Config{
 		ServerName: host,
 	}); err != nil {
-		return nil, zerrors.ThrowInternal(err, "EMAIL-guvsQ", "could not start tls")
+		return nil, zerrors.ThrowInternal(err, "EMAIL-guvsQ", "Errors.SMTP.CouldNotStartTLS")
 	}
 	return client, nil
 }
@@ -154,7 +154,56 @@ func (smtpConfig SMTP) smtpAuth(client *smtp.Client, host string) error {
 	// Auth
 	err := client.Auth(PlainOrLoginAuth(smtpConfig.User, smtpConfig.Password, host))
 	if err != nil {
-		return zerrors.ThrowInternalf(err, "EMAIL-s9kfs", "could not add smtp auth for user %s", smtpConfig.User)
+		return zerrors.ThrowInternal(err, "EMAIL-s9kfs", "Errors.SMTP.CouldNotAuth")
 	}
 	return nil
 }
+
+func TestConfiguration(cfg *Config, testEmail string) error {
+	client, err := cfg.SMTP.connectToSMTP(cfg.Tls)
+	if err != nil {
+		return err
+	}
+
+	defer client.Close()
+
+	message := &messages.Email{
+		Recipients:  []string{testEmail},
+		Subject:     "Test email",
+		Content:     "This is a test email to check if your SMTP provider works fine",
+		SenderEmail: cfg.From,
+		SenderName:  cfg.FromName,
+	}
+
+	if err := client.Mail(cfg.From); err != nil {
+		return zerrors.ThrowInternal(err, "EMAIL-s3is3", "Errors.SMTP.CouldNotSetSender")
+	}
+
+	if err := client.Rcpt(testEmail); err != nil {
+		return zerrors.ThrowInternal(err, "EMAIL-s4is4", "Errors.SMTP.CouldNotSetRecipient")
+	}
+
+	// Open data connection
+	w, err := client.Data()
+	if err != nil {
+		return err
+	}
+
+	// Send content
+	content, err := message.GetContent()
+	if err != nil {
+		return err
+	}
+	_, err = w.Write([]byte(content))
+	if err != nil {
+		return err
+	}
+
+	// Close IO and quit smtp connection
+	err = w.Close()
+	if err != nil {
+		return err
+	}
+
+	return client.Quit()
+}