All Products
Search
Document Center

Direct Mail:Summary of common email return codes and solutions

Last Updated:Dec 18, 2023

Codes of successful email delivery

If an email is sent successfully, DirectMail or the recipient server will return a code: “250 send mail ok”, which indicates that the email request operation is completed, and the email has been sent to the recipient server successfully.

If an email is sent successfully, but the recipient does not receive it. The solution is as follows:

  • Ask the recipient to check whether the email was put into the spam email folder.

  • Ask the recipient to add your sender address to the whitelist, and then send the email again.

  • If the email still cannot be received after adding the sender address to the whitelist, ask the recipient to submit this issue to the email service provider for resolution.

Codes of failed email delivery

If an email fails to deliver, the related error codes will be returned. The 4xx return codes are indicative of temporary errors. The 5xx return codes are indicative of permanent errors. If a temporary error is returned by the recipient server (the return code is 4xx), the email will be resent a few times.

Return codes can differ for each email service providers. They represent different reasons why emails fail to deliver.

Common error codes from DirectMail

Error codes from DirectMail refer to the error codes returned during a mailing request to DirectMail, or the return codes returned by DirectMail during delivery.

Type of return code

Return code

Solution

Authentication failed

535 Authentication failure

Check whether the email sending address or password is correct.

Number of recipient addresses exceeded

556 The number of RCPTs is over the size limit

The recipient address limit has been exceeded.

The limit for one email please refer to Limits. Reduce the number of recipients.

Email size exceeded

557 The length of DATA content has reached the maximum threshold

The email size limit is exceeded. Reduce the size of the email.

Invalid recipient address

559 Invalid rcptto

The recipient address is invalid.

Check whether the address is correct.

MX resolution query failed

423 Dns resolve error

524 Host not found by dns resolve

526 No data by dns resolve

The recipient domain name MX resolution query failed.

Ask the recipient to check the resolution (MX) record of the domain name.

Connection failed

427 Socks Connect to UNREACHABLE host

The target host cannot be reached. This is typically because the resolution (MX) record of the recipient domain name does not exist.

Ask the recipient to check the resolution (MX) record of the domain name.

Email sending quota exceeded

552 Monthly sending quota exceeded

552 Daily sending quota exceeded

552 Not enough sending quota

Email sending quota has been exceeded.

Spam rejection error

554 Reject by content spam

The email has been tagged as a spam email. Modify the content and send again.

Abnormal email sender account status

551 Main account unavailable

The current account is restricted or in an abnormal status.

Log on to the DirectMail console to view the current account status.

Common error codes from the recipient servers

Error codes from the recipient servers refer to the return codes received from the recipient inbox during delivery.

Note: xx represents any symbol; $EMAIL represents email address; $IP represents email sender IP; $DOMAIN represents domain name.

Type of return code

Return code

Solution

Recipient address not found

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 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)

The email return code includes the following information:

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

1. Please check whether the recipient address entered is correct, such as whether there are extra spaces or special characters.

2. Please check whether the recipient's MX resolution is configured correctly. If there is an invalid MX, please contact the recipient's mailbox administrator for handling.

3. Please contact the recipient through other ways to confirm the use status of the mailbox and whether there are expired, disabled or frozen situations.

Account blacklist

550 Mail is rejected by recipients

550 sender in prision

550 User in blacklist

The recipient or the system has blacklisted the sender account.

Ask the recipient to check their blacklist and filter policy.

If the account is not blacklisted, ask the recipient to submit this issue to their email service provider for resolution.

IP blacklist

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

The email return code includes the following information:

denied by RBL

in a DNS blacklist

in the RBL

is filtered by RBL

is listed in RBL

550 Your IP will be reported for abuse - better watch out next time

The email sender IP is blacklisted.Please contact the receiver administrator or service provider for release.

Recipient address confined

450 4.2.1 https://support.google.com/mail/answer/6592

550 Mailbox unavailable or access limited

The recipient has received a large number of emails. To avoid malicious attacks, the recipient address is temporarily confined.

Wait a moment, and then resend the email to the recipient.

IP frequency limit exceeded

421 HL:ICC

421 HL:IFC

421 RP-001

421 RP-002

421 RP-003

550 Connection frequency limited

550 IP frequency limited

The email sender IP frequency limit has been exceeded.

Stop sending emails temporarily, and then retry sending the email.

If the IP frequency exceeds the daily email sending quota, no email is allowed to be sent on that day.

The frequency limit is confidential data belonging to the recipient and is not publicly available.

Email sending account frequency limit exceeded

451 MI:SFQ

550 MI:STC

550 RP:TRC

554 MI:STC

550 Sender frequency limited

The email sending account frequency limit has been exceeded.

Stop sending emails, decrease the frequency, and resend the email later.

If the email sending account frequency exceeds the daily email sending quota, no email is allowed to be sent on that day.

The frequency limit is confidential data belonging to the recipient and is not publicly available.

Email sending domain name frequency limit exceeded

550 Domain frequency limited

Email sending domain name frequency limit has been exceeded.

Stop sending emails, decrease the frequency, and resend the email later.

If the email sending domain name frequency exceeds the daily email sending quota, no email is allowed to be sent on that day.

The frequency limit is confidential data belonging to the recipient and is not publicly available.

Spam 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

The email return code includes the following information:

as spam

is spam

spam denied

spam detected

spam filtering

suspected spam

contain the spam contents

The emails are suspected to be batch emails, are flagged as spam, or have been complained about by multiple users.

Advertisement and promotion emails may only be sent to subscribed recipients. Ask subscribed recipients to add the email sender address to their whitelist.

Ask recipients to add the email sender address for registration and notification emails to their whitelist. If the emails still cannot be received after adding the email sender address to their whitelist, ask the recipient to submit this issue to their service provider for support.

Email size exceeded

550 Message too large

552 Requested mail action aborted: exceeded mailsize limit

The email size is exceeded.

Decrease the email size.

Full mailbox

452 4.2.2 https://support.google.com/mail/?p=OverQuotaTemp

452 4.2.2 https://support.google.com/mail/answer/6558

552 5.2.2 https://support.google.com/mail/answer/6558

550 mailbox limit exceeded

552 mailbox is full

552 5.2.1 Quota exceeded or service disabled

The email return code includes the following information:

is over quota

exceed mailbox quota

The recipient’s mailbox is full.

Ask the recipient to clean up their mailbox.

Recipient temporarily unavailable

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

The recipient system is temporarily unavailable.

Resend the email later.

If resending failed, ask the recipient to submit this issue to the email service provider for resolution.

Account greylisting

450 4.2.0 <$EMAIL>: Recipient address rejected

451 4.7.1 Greylisting in action

451 Grey bounce

The email return code includes the following information:

grey listed

The email sending account is greylisted by the recipient.

Ask the recipient to add the email sender address to the whitelist, and resend later.

If resending failed, ask the recipient to submit this issue to the email service provider for resolution.

Incorrect recipient address format

501 Bad address syntax

550 MI:IMF

The recipient address format is incorrect.

Confirm the correct email address with the recipient.

SPF validation failed

520 ip and spf record not match

550 MI:SPF

550 SPF check failed

SPF is set for the email sending domain name, but fails to validate.

Return codes of some email service providers

Email service provider

Return code description

QQ Mail

https://service.exmail.qq.com/cgi-bin/help?id=20022

https://service.mail.qq.com/cgi-bin/help?id=20022

NetEase Mail

https://qiye.163.com/help/l-9.html

263 Mail

http://www.263.net/263/helpcenter/mailbounce/20150906/842.html

Gmail Mail

https://support.google.com/a/answer/3726730

Microsoft Mail (such as @hotmail.com, @live.com, @live.cn, and @outlook.com)

https://mail.live.com/mail/troubleshooting.aspx#errors

Mimecast

https://community.mimecast.com/s/article/Mimecast-SMTP-Error-Codes-842605754#451