发送邮件过于频繁，超过频率限制，收到退信/报错怎么办？

发送邮件过于频繁，超过频率限制，收到退信/报错怎么办？too frequently sending、much too frequently sending、currently unexpected sending若收到带有这些字样“too frequently sending、much too frequently sending、currently unexpected sending” 的退信