554 5.7.1 DAS41 xx.xx.xx.xx: Your mail is blocked automatically by anti-spam system. (E04)

退信原因：IP被对方列入黑名单中

解决方案：调整其它线路来发送，目前发现连谷歌，雅虎等等发送hanmail.net也经常碰到这样的情况，好像韩国那边比较喜欢屏蔽美国的IP地址，如果你是自架邮局出现这样的问题，可以购买中继来解决这个问题，一般中继服务商都有多个IP不同的机房，一般可以搞定这样的问题

官方说明网址：https://mail.daum.net/policy?category=bulk&tab=returnMessage&language=en

CONNECTION ERROR
421 4.4.1 CHIC IP ADDRESS: Network is busy.
421 4.4.5 CCRT IP ADDRESS: Connection refused. Server is busy(RT)
421 4.4.5 CRCP IP ADDRESS: Connection refused. Server is busy.
421 4.5.0 XTOUT IP ADDRESS: Closing connection by timeout
451 4.4.1 XERR IP ADDRESS: Network is busy(ERROR)
451 4.4.1 XNIOE IP ADDRESS: Network is busy(I/O)
COMMAND ERROR
421 4.7.0 XBCMD IP ADDRESS: Too many bad commands
421 4.7.0 XTCNT IP ADDRESS: Too many transactions
500 5.5.0 XLINE IP ADDRESS: Command line too long
500 5.5.2 XUCMD IP ADDRESS: Command not recognized
501 5.5.4 HARG1 IP ADDRESS: HELO requires domain name
501 5.5.4 HARG2 IP ADDRESS: EHLO requires domain name
501 5.5.4 MARG1 IP ADDRESS: Command argument required
501 5.5.4 RARG1 IP ADDRESS: Command argument required
MAIL COMMAND ERROR
451 4.4.1 DXNS1 IP ADDRESS: Network is busy(XDNS)
451 4.4.1 DXNS2 IP ADDRESS: DNS lookup failed(XDNS)
454 5.7.1 DXNS3 IP ADDRESS: Message refused. Your host name dosen't match with your IP address
501 5.5.4 MARG2 IP ADDRESS: Invalid Mail command argument: ARGUMENT
503 5.5.1 MDUP IP ADDRESS: Sender already specified
503 5.5.1 RMCMD IP ADDRESS: MAIL command required
550 5.1.8 IP ADDRESS: No such user: SENDER ADDRESS
553 5.1.3 RADDR IP ADDRESS: Invalid mail address: SENDER ADDRESS
554 5.7.1 DZCNT IP ADDRESS: Message refused. Your host name(HOST NAME) dosen't match with your IP address.
RCPT COMMAND ERROR
450 4.5.3 RCNT1 IP ADDRESS: Too many recipients
450 4.7.1 MMCNT IP ADDRESS: Message refused. Your IP address has sent too many mails(MAIL COUNT).
501 5.5.4 RARG2 IP ADDRESS: Invalid RCPT command argument: ARGUMENT
552 5.2.2 RFULL IP ADDRESS: Mailbox is full: RECIPIENT ADDRESS
550 5.1.1 MUSR IP ADDRESS: No such user: RECIPIENT ADDRESS
550 5.1.1 RUSR IP ADDRESS: No such user: RECIPIENT ADDRESS
550 5.2.1 DDENY IP ADDRESS : The receiver denied your mail. Please contact the receiver with another way.: XXXX@hanmail.net
550 5.2.1 RACT IP ADDRESS: Mailbox is inactive: RECIPIENT ADDRESS
550 5.7.1 RDENY IP ADDRESS : The receiver denied your mail. Please contact the receiver with another way.: XXXX@hanmail.net
553 5.1.7 MADDR IP ADDRESS: Invalid mail address: SENDER ADDRESS
DATA COMMAND ERROR
451 4.3.0 RTEMP IP ADDRESS: Temporary home error: RECIPIENT ADDRESS
451 4.4.1 DNIOE IP ADDRESS: Network is busy(I/O)
451 4.4.1 DTOUT IP ADDRESS: Network is busy(I/O:timeout)
554 5.4.5 DDOT IP ADDRESS: Message not terminated by end with "." on a line by itself
554 5.4.6 DLOOP IP ADDRESS: Routing loop detected
554 5.4.6 DSIZE IP ADDRESS: Message size exceeds the limit(LIMIT)
554 5.6.0 DHFR2 IP ADDRESS: Invalid 'From' header: FROM
554 5.7.1 CCRX IP ADDRESS: Connection refused. Your IP address is blocked(anti-spam)
554 5.7.1 DAS41 IP ADDRESS: Your mail is blocked automatically by anti-spam system. (E04)
554 5.7.1 DAS50 IP ADDRESS: Your mail is blocked automatically by anti-spam system. (E05)
554 5.7.1 SAS41 IP ADDRESS: Your mail is blocked automatically by anti-spam system. (E04)
554 5.7.1 SAS50 IP ADDRESS: Your mail is blocked automatically by anti-spam system. (E05)