[1、extend和vendor的区别](extend%E5%92%8Cvendor%E7%9A%84%E5%8C%BA%E5%88%AB.md) [2、发送邮件](2%E3%80%81%E5%8F%91%E9%80%81%E9%82%AE%E4%BB%B6.md)