最新版本的邮件群发软件对于发送失败的电子邮件，将详细的错误编码也显示出来了；以前这些信息只是记录在后台的日志中，没有在界面上显示出来。那么这些错误码究竟代表什么意思呢？我们这里做了列举。

512 "Unexpected SMTP Login response";
513 "Failed to get header of body part";
514 "Failed to get body of body part";
515 "Failed to ger footer of body part";
516 "Unexpected EHLO response";
517 "Unexpected HELO response";
518 "Unexpected QUIT response";
519 "Unexpected MAIL FROM response";
520 "Unexpected DATA response";
521 "Unexpected End of Message response";
522 "File too large to mail";
523 "Cannot mail 0 byte length file";
524 "Unexpected RCPT TO response";
525 "Unexpected AUTH LOGIN response";
526 "Unexpected AUTH LOGIN username request";
527 "Unexpected AUTH LOGIN username response";

528 "Unexpected AUTH LOGIN password request";
529 "Unexpected AUTH LOGIN password response";
530 "Unexpected AUTH PLAIN response";
531 "Unexpected AUTH PLAIN username request";
532 "Unexpected AUTH PLAIN username response";
533 "Unexpected AUTH PLAIN password request";
534 "Unexpected AUTH PLAIN password response";
535 "Unexpected CRAM-MD5 response";
536 "Unexpected CRAM-MD5 digest response";
537 "Failed to perform NTLM authentication";
538 "Unexpected AUTH NTLM response";
539 "Failed to base64 decode data";
540 "Failed to base64 encode data";
541 "Failed to create SSL socket";
542 "Failed to connect to Socks 4 proxy via SSL";
543 "Failed to connect to Socks 5 proxy via SSL";

544 "Failed to connect to HTTP proxy via SSL";
545 "Failed to connect via SSL";
546 "Failed to send data via SSL";
547 "Failed to receive data via SSL";

这些错误代码只是详细记录SMTP服务器（即：邮件发送服务器）返回的具体内容，如果您对SMTP协议比较了解，这些错误代码对您有一定的帮助，但是意义不大。这是发送服务器根据你的发送情况对的发送请求做的一些限制。
只要不是SMTP服务器的用户名和密码错误，完全可以忽略这些具体的错误号，而将“失败”列表中的内容导出来再次发送即可。如果某类服务器总是出现这样的错误，可能是Email账号暂时被禁用，或者邮件内容和附件中包含了SMTP服务器认为不能投递的内容，可以试着换其他邮箱服务器发送。