在做邮件营销的推广的过程中，邮件退信率是一个重要的指标。

邮件退信率会影响到发邮件的域名，IP的信誉值，退信率越高域名IP的信誉值越低，邮件将直接进入垃圾箱。

根据EmailDiamond的数据分析，电子邮件的退信率上升的主要原因在于：

1、收件人邮箱地址不存在。

2、收件人邮箱错误

3、邮箱域名不存在

4、MX记录不存在

5、邮件列表存在陷阱邮件地址

6、收件人的地址为一次性的地址

常见的退信代码：

521 Recipient address rejected

550 5.1.1 https://support.google.com/mail/?p=NoSuchUser

550 5.1.1 https://support.google.com/mail/answer/6596

550 Invalid User

550 Mailbox not found

550 user not exist

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)

421 4.7.0 [xx] Message from ($IP) temporarily deferred

421 4.7.0 [xx] Message temporarily deferred

421 4.7.0 https://support.google.com/mail/answer/188131

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

423 Dns resolve error

524 Host not found by dns resolve

526 No data by dns resolve

EmailDiamond总结了以下几种避免邮件退信技巧

1、确保邮箱地址正确

2、过滤掉陷阱邮箱

3、确保邮箱地址经过验证和清洗

4、优化发信邮箱的域名信誉值

5、避免发信IP进入反垃圾邮件黑名单