Auto Email Sender

After sending mass emails, you may receive some server return emails with title "Mail delivery failed: returning message to sender". Want to know why this happens and how to solve? This article will show you all 14 reasons of mail delivery failure and return email messages, and guide you how to solve these issues.

The system returned email is that the sending mail server (SMTP server) cannot send the email to the destination correctly. It reminds you by sending you a message. The message would contain the following information:

1. The email address that was not sent successfully.

2. The specific reason for the return email.

There are many specific reasons for the return email, which will be listed below, but the most common one is that the other party's email address is invalid, which means that the email address is no longer available, or does not exist at all, or has been banned.

How to use the following information: There must be many reasons for the same in the received return email, and the same error has been found more frequently. According to the keywords in the error reason, search from this article and solve it according to the solution (possibly There is no need to solve it at all).

The specific reason for the return email:

1. The recipient address does not exist

The Cause of the error:
The recipient's email account does not exist or the recipient's server cannot find the recipient's email address

Keywords that may appear in the return email:
No such user, user unknown, unknown or illegal alias, account inactive, user not found, Invalid address, invalid recipient, not a valid mailbox, mailbox cannot be delivered

Solution:
Since the user email address to be delivered cannot be found on the website, the email cannot be delivered to the address correctly for the recipient to receive this return. It may be due to a wrong email address. Please confirm that the address is entered correctly, or confirm with the recipient what the correct email address is. Resend the email after the confirmation.

2. The recipient's mailbox is disabled

Cause of error:
The recipient user's mailbox is disabled or unavailable, may have not been logged in and used for a long time, or the account has been frozen due to reasons such as failure to pay.

Keywords that may appear in the return email:
disabled

Solution:
Contact the recipient and ask him to contact his mailbox system administrator to confirm the recipient's mailbox problem.

3. Insufficient space in recipient mailbox

The Cause of the error:
The recipient does not have enough mailbox space to accept new mail

Keywords that may appear in the return email:
mailbox is full, exceeded, hard limit

Solution:
The recipient's mailbox has not enough free space to receive your mail. Please use other methods to contact the recipient and remind to clear the useless mail in the mailbox and make space for new emails.

4. Mail is filtered

The reason for the error:
The server of the recipient has restricted the received emails, and your email exceeds the request of the other party or the request of the other party's server.

Keywords that may appear in the return email:
not welcome, content rejected, Message blocked, Recipient reject, No welcome message from****, Mail refused/Box is busy

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 mail you send is such as "sender name, personal 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 recipient's system after delivery.

Please make appropriate changes to the email content you send, such as the subject sent. If you still can't send normally after trying, it's best to contact the recipient by other methods, and provide the return information to the recipient to find out what kind of filtering rules are met. After confirmation, you can send it normally after making appropriate modifications.

5. Error in domain name resolution

Cause of the error:
There is an error in the recipient's server or the domain name, or the domain name information cannot be correctly resolved by the internet DNS system, and the recipient's mail server IP cannot be found, resulting in delivery errors. Another possibility is that the network problem of your own server makes it impossible to query the recipient's domain name, or the DNS failure.

Keywords that may appear in the return email:
Host, not found, bad host, domain, unreachable, Connection refused

Solution:
First, please check whether there is a spelling error when entering the recipient's email address. After confirming the error, resend it to solve it. Quite a few return emails have such a situation.

6. Unrecognized command

The reason for the error:
Unable to recognize the wrong command (mail system command)

Keywords that may appear in the return email:
error in command, syntax error, Error email address format

Solution:
The reason is mostly because the software used by the sender or the sending server is connected to the recipient's server for delivery, and the recipient's system cannot recognize the software or the sender's server's instructions, resulting in a sending error.

Sometimes, because the sender enters illegal characters such as double quotes", slash/, ^ and other illegal characters when filling in the recipient's email address, it can also cause this type of unsuccessful transmission.

7. The size of the sent mail exceeds the maximum limit

The reason for the error:
The recipient's mail system service provider rejected the mail because the sender's mail was too large

Keywords that may appear in the return email:
exceeds, maximum message size, Data size

Solution:
Usually this kind of error is because the recipient's mail system does not support users in their system to receive too large email.

8. Mail is rejected

Reason for error:
The sender's mail was rejected by the receiver's mail service provider

Keywords that may appear in the return email:
banned, isn't in my list of allowed rcpthosts, domain is not welcome, Connection refused, Relaying denied, spam, spammers

Solution:
The mail sent from this place is rejected because the email address, domain or IP address sent by the recipient's system is included in the rejection list.

9. Failed to connect to the recipient's server

The Cause of the error:
The mail server of the other party was found when the system was sending mail, but because the internet network is abnormal or the mta service of the recipient server is abnormal, the response from the recipient's mail server cannot be obtained normally, that is, the recipient's server is not responding.

Keywords that may appear in the return email:
Connection timed out, Connect to xxx.xxx.xx.xx: 25 failure, Error sending mail body to ******, Failure welcome message from

Solution:
Use nslookup to find the mail server IP pointed to by the MX record of the recipient's domain name, and use telnet to confirm whether the network connection is abnormal or the 25 port of recipient server is not responding. Generally speaking, whether it is a network failure or a system failure of the recipient's server, the system administrator of the recipient is quickly discovered and recovered, so you can choose to send it again later. For some countries' email service providers, this situation will last for a long time. If the attempt fails for more than 1 day, it is recommended to use other methods to contact the recipient.

Make sure your machine can connect to the external host correctly, and finally test whether it can connect to the host that failed to send successfully (the prompt with a string beginning with 220 appears).

10. The number of recipients of a single email exceeds the limit

Reason:
There are too many recipients for a single message

Keywords that may appear in the return email:
Too many, less than xx

Solution:
The mail system will account for the number of multiple users who post the same email each time each email sender connects. Therefore, when someone sends bulk of emails, the recipient server will reject the message or return an error message such as "Too many recipients". . Therefore, you should try to keep the number of receiving users at about 20-30 when each email is delivered. If the quantity of contacts is large, you should send them in batches.

11. Anti-spam list

The reason for the error:
The address of the sending server was added to the blacklist of some anti-spam organizations, resulting in rejection

Keywords that may appear in the return email:
Mail from ***.***.***.*** refused, see http://**************

Solution:
Many anti-spam organizations have directly blacklisted the IP addresses of many other regions and countries. It may not be reasonable for them to block your IP addresses. Many anti-spam organizations have blacklisted the entire IP address of some regions. Generally this kind of return email will include a link, you can apply to remove your mail server IP address from the list according to the requirements on the website.

12. DNS reverse resolution

The reason for the error:
In order to prevent spam, some mail servers perform a DNS reverse lookup on the sender's email address when receiving mail. The mails of the sender with correct DNS resolution on the public network are released, but for the DNS reverse Resolve incorrect addresses to block them.

Keywords that may appear in the return email:
can't verify FROM domain in DNS, domain does not exist

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 recipient reverses the resolution and cannot return the query normally. If the recipient's mail system has such a verification mechanism, the return will occur.

When confirming that the return mail 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.

13. IP Reverse resolution

Reason for error:
In order to prevent spam, some mail servers perform IP DNS reverse query to the sending host when receiving mail, and release the mail with the correct IP resolved by ptr.

Keywords that may appear in the return email:
doesn't have correct PTR record, cannot find your hostname

Solution:
Add mail server to fix IP reverse analysis.

14. Relay sending error

The reason for the error:
Relay sending is used in Winmail, but there is a problem with the relay setting, which makes it impossible to send.

Keywords that may appear in the return email:
relay server said: 535 auth failure

Solution:
Check the relay settings to make sure if the authentication account and password are correct. Is the relay server address correct? Can the server connect to the relay server?



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