Add support for **Implicit TLS (SMTPS)** to the SMTP email service

app/pkg/env/env.go

@@ -117,11 +117,12 @@ type config struct {
 			Region string `env:"EMAIL_MAILGUN_REGION,default=US"` // possible values: US or EU
 		}
 		SMTP struct {
-			Host           string `env:"EMAIL_SMTP_HOST"`
-			Port           string `env:"EMAIL_SMTP_PORT"`
-			Username       string `env:"EMAIL_SMTP_USERNAME"`
-			Password       string `env:"EMAIL_SMTP_PASSWORD"`
-			EnableStartTLS bool   `env:"EMAIL_SMTP_ENABLE_STARTTLS,default=true"`
+			Host              string `env:"EMAIL_SMTP_HOST"`
+			Port              string `env:"EMAIL_SMTP_PORT"`
+			Username          string `env:"EMAIL_SMTP_USERNAME"`
+			Password          string `env:"EMAIL_SMTP_PASSWORD"`
+			EnableStartTLS    bool   `env:"EMAIL_SMTP_ENABLE_STARTTLS,default=true"`
+			EnableImplicitTLS bool   `env:"EMAIL_SMTP_ENABLE_IMPLICIT_TLS,default=false"`
 		}
 	}
 	BlobStorage struct {

app/services/email/smtp/smtp.go

@@ -100,25 +100,42 @@ func sendMail(ctx context.Context, c *cmd.SendMail) {
 		smtpConfig := env.Config.Email.SMTP
 		servername := fmt.Sprintf("%s:%s", smtpConfig.Host, smtpConfig.Port)
 		auth := authenticate(smtpConfig.Username, smtpConfig.Password, smtpConfig.Host)
-		err = Send(localname, servername, smtpConfig.EnableStartTLS, auth, email.NoReply, []string{to.Address}, b.Bytes())
+		err = Send(localname, servername, smtpConfig.EnableStartTLS, smtpConfig.EnableImplicitTLS, auth, email.NoReply, []string{to.Address}, b.Bytes())
 		if err != nil {
 			panic(errors.Wrap(err, "failed to send email with template %s", c.TemplateName))
 		}
 		log.Debug(ctx, "Email sent.")
 	}
 }
 
-var Send = func(localName, serverAddress string, enableStartTLS bool, a gosmtp.Auth, from string, to []string, msg []byte) error {
+var Send = func(localName, serverAddress string, enableStartTLS, enableImplicitTLS bool, a gosmtp.Auth, from string, to []string, msg []byte) error {
 	host, _, _ := net.SplitHostPort(serverAddress)
-	c, err := gosmtp.Dial(serverAddress)
-	if err != nil {
-		return err
+
+	var c *gosmtp.Client
+	var err error
+
+	if enableImplicitTLS {
+		// Implicit TLS (SMTPS): wrap connection in TLS before any SMTP command.
+		// Typically used on port 465.
+		conn, err := tls.Dial("tcp", serverAddress, &tls.Config{ServerName: host})
+		if err != nil {
+			return err
+		}
+		c, err = gosmtp.NewClient(conn, host)
+		if err != nil {
+			return err
+		}
+	} else {
+		c, err = gosmtp.Dial(serverAddress)
+		if err != nil {
+			return err
+		}
 	}
 	defer func() { _ = c.Close() }()
 	if err = c.Hello(localName); err != nil {
 		return err
 	}
-	if enableStartTLS {
+	if enableStartTLS && !enableImplicitTLS {
 		if ok, _ := c.Extension("STARTTLS"); ok {
 			config := &tls.Config{ServerName: host}
 			if err = c.StartTLS(config); err != nil {

app/services/email/smtp/smtp_test.go

@@ -29,7 +29,7 @@ var ctx context.Context
 
 var requests = make([]request, 0)
 
-func mockSend(localname, servername string, enableStartTLS bool, auth gosmtp.Auth, from string, to []string, body []byte) error {
+func mockSend(localname, servername string, enableStartTLS, enableImplicitTLS bool, auth gosmtp.Auth, from string, to []string, body []byte) error {
 	requests = append(requests, request{servername, auth, from, to, body})
 	return nil
 }