Close SMTP data before quit

main.go

@@ -636,7 +636,6 @@ func sendEmail(cfg Config, subject, body string) error {
 	if err != nil {
 		return err
 	}
-	defer writer.Close()
 
 	headers := textproto.MIMEHeader{}
 	headers.Set("From", cfg.EmailFrom)
@@ -655,6 +654,9 @@ func sendEmail(cfg Config, subject, body string) error {
 	if _, err := io.WriteString(writer, "\r\n"+body); err != nil {
 		return err
 	}
+	if err := writer.Close(); err != nil {
+		return err
+	}
 	return conn.Quit()
 }