Explicitly decide whether to use TLS in mailer's configuration (#5024)

* explicitly decide on using TLS for mail connections

* explicitly decide on using TLS for mail connections

* keep compatibility

modules/mailer/mailer.go

@@ -122,11 +122,10 @@ func (s *smtpSender) Send(from string, to []string, msg io.WriterTo) error {
 	}
 	defer conn.Close()
 
-	isSecureConn := false
+	isSecureConn := opts.IsTLSEnabled || (strings.HasSuffix(port, "465"))
 	// Start TLS directly if the port ends with 465 (SMTPS protocol)
-	if strings.HasSuffix(port, "465") {
+	if isSecureConn {
 		conn = tls.Client(conn, tlsconfig)
-		isSecureConn = true
 	}
 
 	client, err := smtp.NewClient(conn, host)