Under normal circumstances, when the email you send cannot reach the recipient’s mailbox normally, the Email system will automatically send you a warning letter. The bounce notification contains the reason why it cannot be sent to the recipient’s email address normally, so most In this case, you can use the bounce notification to find out the reason and solution for the failure of sending the letter. Here is an introduction to common reasons and solutions for e-mail bounces
. 1. The other user does not have
keywords No such user, user unknown, unknown or illegal alias, account inactive, user not found, Invalid address, invalid recipient, not a
Examples of valid mailbox, mailbox cannot be delivered return letter
no mailbox here by that name
return letter reason: the other party’s mailbox account does not exist.
Because the user address to be delivered cannot be found on the website, the mail cannot be delivered correctly In the address to let the recipient receive this bounce letter. It may be due to a wrong email address. Please confirm that the address is entered correctly, or confirm with the recipient whether the email address is. Re-delivery after confirmation.
2. Account is disabled (frozen or deleted, etc.)
return letter example
User ***@163.net is disabled:
host mta.21cn.com[22.214.171.124] said: 550 is now disabled with SMTP service.:
host……said: 554 delivery error:
*** Sorry your message to ***@yahoo.com.cn cannot be delivered. This account has been disabled or discontinued.-mta582.mail.yahoo.com
reason for return: Receive The user’s mailbox is disabled or unavailable. It may be that the mailbox account has been frozen because it has not been logged in for a long time, or has not been paid.
1. If there is no mailbox permission, there are three situations:
a. Free mail —If you have not logged in to the mailbox for more than a certain period of time, the mailbox function will be cancelled.
b. Charged mail—The expiration date has expired, but the receipt of your mailbox fee has not been confirmed.
c. Violation of the mailbox service agreement (such as sending LJ indiscriminately) Letters, etc.) 2. If the recipient is an account of another mail system (foreign domain): Please contact the other party or the other party’s system administrator to confirm.
3. The other party’s mailbox is not enough to receive new mail
keywords Quota, exceded, hard limit, Exceeding, storage allocation
return letter example
Quota exceed the hard limit for user ***@163.net:
Host …… said: 552 This person’s account is exceeding their quota.:
Exceeded storage allocation: 552 Channel Size Limit exceeded
Bounce reason: The recipient has insufficient mailbox space to accept new mail.
recipient’s mailbox has insufficient free space to receive your mail. Please use other methods to contact the recipient. Please clear the mailbox first. Useless emails, make room to receive new emails.
4. The other party rejects the email
keywords not welcome, content rejected, Message blocked, Recipient reject.
Examples of bounce letters
This Message is not welcome:
Error: content rejected:
Message content rejected:
Message blocked .:
host ……said: 550 Recipient reject ：550 CoremailSys: Your message was blocked by NetEase AntiSpam+. The
reason for the return letter: the recipient does not have enough mailbox space to accept new mail.
Solution: “not Welcome”, “message blocked” and “content rejected” appear mainly because the recipient has set a filter in the mailbox, and the mail you send is such as “sender” and “receiver” One or several of “Subject” and “Mail Volume” just meet the recipient’s condition filtering, which results in the mail being rejected by the other party’s system after delivery. Please make appropriate changes to the mail you send, such as the “subject” you send, try to use more neutral words. Such as “Hello” and so on. Control the volume of emails not to be too large, because users can limit the size of emails in the filter. If there is an error in the delivery of a relatively large email, you can compress the attachments in the email with compression software before processing. The “message blocked” situation may also be due to the other server restricting the sending of the sender’s mail.
5. Unable to find the other’s server name (domain name or host)
keyword Host, not found, bad host, domain, unreachable, Connection refused to
return Letter example
Name service error for domain sian.com:
Host not found:
Name service error for domain zdl.net:
Host not found, try again:
Name service error for domain hot.163.net:
Host not found: bad host/domain syntax: “.
(****@shou.com): connect to shou.com: Connection refused: domain unreachable (the email system of the domain @263.com does not exist)
reason for the return letter: the host or the other party’s domain name is wrong, or cannot be correct Is explained by the system, and most of the delivery errors are caused by the wrong domain name behind @.
Solutions: “host not found” and “domain syntax” are mainly due to the fact that the user writes the other party’s email address when writing the other party’s email address. The host and domain name behind @” are incorrectly written, such as “sina.com” is incorrectly written as “@sian.com”, or the original “@163.net” is incorrectly written as “@hot.163.net” because of 163. There is no “hot” host in the net, so an error occurs. Similarly, add more “.” between @ and domain name.
6. System command error
keyword error in command, syntax error
return letter example
Host ……said: 500 error in command (“”email@example.com??iwalom0681″”@sina.com): host ……said : 555 ******??-syntax error (#5.5.4) The
reason for the return letter cannot be recognized. Error command (mail system command)
The reason is mostly because the software used or the sending system is connected to the other party’s system for delivery, and the other party’s system cannot recognize the software or the instruction system of the sender’s system, resulting in a sending error. Please use commonly used software such as Outlook Express or Foxmail to edit emails, or send emails directly by WEB, which can reduce the chance of errors. If the problem persists, please resend it at a later time. The second type is used when the sender enters illegal characters such as “”” “/” “” “^” and other illegal characters when filling in the recipient’s address, resulting in failure to send successfully.
Seven, the content of the sent mail contains sensitive Words and
keywords Box is busy
return letter example
Host ……said: 450 Fail, Box is busy
return letter reason: The content of the mail is sensitive and there is an error. (Mail system instructions).
Solution: Because the system will use Outlook Express and Emails sent by mail client software such as Foxmail are subject to content filtering, so users will make mistakes when sending sensitive words or sentences, causing them to fail to be sent. Please check the contents of the emails to ensure that the emails are sent smoothly.
8. Sending The email is too large, causing the recipient’s server to reject the
keyword “exceeds”, “maximum message size”, and “Data size”
return letter. Example:
552 Message size exceeds fixed maximum message size: 7372800 bytes: 552 5.2.3 Message size exceeds fixed maximum
message size (7200000): host smtp.xaonline.com[126.96.36.199] said: 552 Data size must not exceed 4096K bytes. Bounce
reason: The recipient’s system service provider rejected the email because the sender’s email volume was too large .
Solution: Usually this kind of error is due to the restriction made by the protection mechanism adopted by the recipient’s system that does not allow users in their system to receive oversized emails. Therefore, users can use Outlook Express’s mail splitting function to split and send oversized emails. The blue text indicates the maximum capacity that the other party can only receive for each email.
9. The recipient’s system service provider refuses to accept this email.
Keyword banned, isn’t in my list of allowed rcpthosts, domain is not welcome, Connection refused, Relaying denied
Examples of return letters:
571 ***@163.net.. . from mail01j.rapidsite.net You are banned, contact yourlocal admin.:
553 sorry, that domain isn’t in my list of allowed rcpthosts (#5.7.1):
550… Relaying denied: 550 5.0.0) ( #####@163.net):
Mail originating from that domain is not welcome here: connect to mf2.XXXXX.com: Connection refused
Reason for return letter: Because the sender’s mail was rejected by the receiver’s system service provider.
Solution: Because the other party’s system included the sending address, domain or IP address in the rejection list, the mail sent from this place was rejected. If you encounter this situation, you can send the content you sent, the sending address, and the sending time to our administrator, so that our administrator can contact the other party’s administrator as soon as possible, and it has been resolved as soon as possible. Please use other methods to contact them first. If you need to send an email urgently, please use another email address to send it first.
10. The size of the sent mail exceeds the maximum limit.
Keyword exits, maximum message size, and Data size
return letter Example: sorry, the message size exceeds databytes limit
Reason for return letter: The sender’s mail is too large and the recipient’s mail system service provider rejects it. Receive this email.
Solution: Usually this kind of error is because the recipient’s mail system does not support users in their system to receive too much mail. Therefore, users can split and send oversized email attachments using Outlook Express’s email splitting function. Usually the number that follows is the size of a single mail that the other party’s system is allowed to receive.
11. Connection timed out
Connection timed out
bounce back example
Connect to iris.sipp.ac.cn:
Connection timed out:
No found target server
1. The connection to the other party’s server has timed out. (In this case, the domain name exists in the mail system, but the network cannot be connected temporarily)
2. It may be the other party’s domain name There is no mail system on the Internet, so I can’t connect.
1. The main reason is that the timeout occurs when the connection is sent due to the network during the connection with the other party’s server, which leads to an error in the delivery of this mail. Please try the delivery of this email again at a later time.
2. Please confirm whether the address of the other party exists and whether there is any wrong address. Or you can check whether you can find the MX pointing record of the other party’s domain name by NSLOOKUP and the correct mass mailing contains too many users.
key to the number of recipients of a single email exceeds the limit
Examples of bounce letters with the words Too many, less than xx : sorry, too many recipients,
bounce reason: a single message has too many recipients.
Solution: the mail system will respond to the number of the same message each time a mail deliverer connects. Voting the number of users, so when users use mass messaging, there will be rejections or wrong information returned such as “Too many recipients” information. Therefore, users should try to keep the number of receiving users at about 20-30 when each mail is delivered. If the receiving volume is large, you can send it several times.
13. Mail is filtered
Keywords: not welcome, content rejected, Message blocked, Recipient reject, No welcome message from****, Mail refused/Box is busy
return letter Example: delivery failure: the message matches up to the filter rule(level: system, name:xxx)
Reason for returning the letter: The other party has restricted the accepted emails, and your email exceeds the request of the other party or the request of the other party’s server.
Solution: The reason for messages such as not Welcome/message blocked/content rejected is that the recipient has set some filtering rules in the mailbox, and the information in the email you sent is such as “sender name” and “sender” The information in “address”, “email subject”, “email body”, “attachment”, etc. complies with the filtering rules set by the recipient or the recipient’s service provider, which results in the mail being rejected by the other party’s system after delivery.
Please make appropriate changes to the mail you send, such as the “email subject” sent. If you tried to send was not normal, it is best to contact the recipient by other means, to provide information to the recipient bounce specific query is in line with what kind of filter rules, with appropriate modifications can be normal after confirmation sent
fourteen , Anti-spam list
keywords: Mail from ***.***.***.*** refused, see https://**************
Return letter example: 554 5.7.1 Rejected xxx.xxx.xxx.xxx found in dnsbl.sorbs.
Solution: Many foreign anti-spam organizations also directly blacklist the IP addresses of many regions in China. It may not be reasonable for them to block China’s IP addresses. Many anti-spam organizations blacklist the entire IP address of China. List.
When you encounter this situation, you can contact the anti-spam organization and try your best to solve such problems.
15. DNS reverse analysis
keywords: can’t verify FROM domain in DNS, domain does not exist
bounce letter Example: 554 refused’mail from’ because return MX does not exist
bounce letter reason: some mail servers are to prevent spam For mail needs, when receiving mail, perform a DNS reverse lookup on the sender’s email address, release mail from senders with correct DNS resolution on the public network, and block addresses with incorrect reverse DNS resolution.
Solution: Most of these problems are corporate mailbox users with their own domain names. This type of server requires that the relevant SOA records and MX records in the domain name resolution settings used by the users are correct and can be queried. Therefore, the DNS resolution record is incomplete or the mail server where the domain name is located fails when the other party reverses the resolution and cannot return the query normally. If the recipient’s mail system has such a verification mechanism, such a bounce will occur. When confirming that the bounce letter is due to the above reasons, notify the administrator of your domain name server to check and confirm your domain name resolution record information or wait until the domain name server is normal to send it normally. The method to check whether the MX record exists, domain name information query.