我们在做EDM的时候，电子邮件发送成功率是重要指标之一。除了软弹回和硬弹回统计，发送系统往往会提供给我们更详细的退信原因，如下所示email退信代码。仔细查看退信原因并找到解决方法可以大大提高邮件营销成功率及营销效果。并且能保证整个邮件发送通道的健康和持续。
| 分类 | 退信代码 |
| 认证失败 | 535 Authentication failure |
| 收件地址数量超限 | 556 The number of RCPTs is over size |
| 邮件大小超限 | 557 The length of DATA content is achieved the maximum threshold |
| 命中无效地址库 | 559 Invalid rcptto |
| 收信域名 MX 解析查询失败 | 423 Dns resolve error 524 Host not found by dns resolve 526 No data by dns resolve |
| 连接失败 | 427 Socks Connect to UNREACHABLE host |
| 发信额度超限制 | 552 Monthly sending quota exceeded 552 Daily sending quota exceeded 552 Not enough sending quota |
| 反垃圾类错误 | 554 Reject by content spam |
| 发信账户状态异常 | 551 Main account unavailable |
| 接收地址不存在 | 521 Recipient address rejected 550 5.1.1 550 Invalid User 550 Mailbox not found 550 user not exist 550 User not found 554 delivery error: dd Sorry your message to $EMAIL cannot be delivered. This account has been disabled or discontinued 554 delivery error: dd This user doesn’t have a $DOMAIN account ($EMAIL) 退信代码包含如下信息： account does not exist invalid address invalid mailbox invalid recipient invalid user is not a valid mailbox is not a valid user mailbox not found no mailbox by that name no mailbox here by that name no such address no such mailbox no such recipient no such user recipient does not exist recipient is not exist recipient not found recipient unknown unknown or illegal alias unknown user user not exist user not found user unknown |
| 账号黑名单 | 550 Mail is rejected by recipients 550 sender in prision 550 User in blacklist |
| IP 黑名单 | 450 DT:RBL 554 HL:IPB 550 DY-001 550 DY-002 550 OU-001 550 OU-002 550 SC-003 550 SC-004 550 in an RBL 550 ip in prision 550 Your IP address is blacklisted 550 5.7.1 Service unavailable; client [$IP] blocked using $DOMAIN 553 5.7.1 [BLxx] Connections will not be accepted from $IP 554 5.7.1 Client host [$IP] blocked using $DOMAIN 550 5.7.1 Mail from IP $IP was rejected due to listing in Spamhaus SBL 550 IP $IP is blocked 554 IP in blacklist 598 ip address in blacklist 退信代码包含如下信息： denied by RBL in a DNS blacklist in the RBL is filtered by RBL is listed in RBL |
| 接收地址被限制 | 450 4.2.1 550 Mailbox unavailable or access denied |
| IP 频率超限 | 421 HL:ICC 421 HL:IFC 421 RP-001 421 RP-002 421 RP-003 550 Connection frequency limited 550 IP frequency limited |
| 发信账号频率超限 | 451 MI:SFQ 550 MI:STC 550 RP:TRC 554 MI:STC 550 Sender frequency limited |
| 发信域名频率超限 | 550 Domain frequency limited |
| 垃圾邮件 | 421 4.7.0 [xx] Message from ($IP) temporarily deferred 421 4.7.0 [xx] Message temporarily deferred 450 Requested action not taken 451 DT:SPM 550 DT:SPM 550 SC-001 521 5.2.1 : AOL will not accept delivery of this message 550 5.7.1 Message rejected as spam by Content Filtering 550 Mail content denied 550 Suspected spam 554 Message not allowed 退信代码包含如下信息： as spam is spam spam denied spam detected spam filtering suspected spam contain the spam contents |
| 邮件大小超限 | 550 Message too large |
| 邮箱空间满 | 452 4.2.2 552 5.2.2 550 mailbox limit exceeded 552 mailbox is full 552 5.2.1 Quota exceeded or service disabled 退信代码包含如下信息： is over quota exceed mailbox quota |
| 接收方临时故障 | 400 the mta server of unexpected closed 450 Service temporarily unavailable 451 $DOMAIN Resources temporarily unavailable 451 4.7.1 Sorry, the service is currently unavailable 451 Internal resource temporarily unavailable 451 Resources temporarily not available 451 Temporarily unable to process your email |
| 账号灰名单 | 450 4.2.0 <$EMAIL>: Recipient address rejected 451 4.7.1 Greylisting in action 451 Grey bounce 退信代码包含如下信息： grey listed |
| 接收地址格式错误 | 501 Bad address syntax 550 MI:IMF |
| SPF 验证失败 | 520 ip and spf record not match 550 MI:SPF 550 SPF check failed |
| 网络异常 | 400 the mta server of unexpected closed |
| 连接失败或者MX 解析查询失败 | 427 Socks Connect to 423 Dns resolve error |
| 流控 | has been temporarily rate limited |
| 无效地址 | 554 delivery error: dd |
| 收信系统灰名单机制 | 含有 GreyListed try again later come back later Internal resource temporarily unavailable |