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It is important to figure out why your email bounces. If you receive an email bounce, you can look in the bounce message to find the proper error code that will give you the reason for the bounce. Below is a list of the Standard SMTP error codes and the Extended SMTP (ESMTP) error codes.

SMTP Error Codes

This list of codes is the standard SMTP error codes you will find in most email bounces.

200 Codes

  • 211 - System status / system help reply
  • 214 - Help message
  • 220 - Domain service ready
  • 221 - Domain service closing transmission channel
  • 250 - Requested mail action completed and OK
  • 251 - Not Local User, forward email to forward path
  • 252 - Cannot Verify user, will attempt delivery later
  • 253 - Pending messages for node started

300 Codes

  • 354 - Start mail input; end with .
  • 355 - Octet-offset is the transaction offset

400 Codes

500 Codes

Extended SMTP (ESMTP) standards

The Extended SMTP error codes work in 3 digit combinations. For example, 5.2.1 is a Permanent Error where the receiving email is not accepting messages. The first number is the email message status. The second 2 numbers pinpoint the exact information bout the error.

  • 2 Successfully sent the email;
  • 4 Temporary problem when sending the email. The email server typically will try to send it again till it reaches retry timeout.
  • 5 Permanent or Fatal error. This can be caused by a non existent email address, DNS problem, or your email was blocked by the receiving server.

Below is a list of the Extended SMTP error codes.

Note! X can be a 4 or a 5 depending on is its Temporary or Permanent.

x.1.x Codes

  • X.1.0 - Other address status
  • X.1.1 - Bad destination mailbox address
  • X.1.2 - Bad destination system address
  • X.1.3 - Bad destination mailbox address syntax
  • X.1.4 - Destination mailbox address ambiguous
  • X.1.5 - Destination mailbox address valid
  • X.1.6 - Mailbox has moved
  • X.1.7 - Bad sender's mailbox address syntax
  • X.1.8 - Bad sender's system address

x.2.x Codes

  • X.2.0 - Other or undefined mailbox status
  • X.2.1 - Mailbox disabled, not accepting messages
  • X.2.2 - Mailbox full
  • X.2.3 - Message length exceeds administrative limit
  • X.2.4 - Mailing list expansion issue

x.3.x Codes

  • X.3.0 - Other or undefined mail system status
  • X.3.1 - Mail system full
  • X.3.2 - System not accepting network messages
  • X.3.3 - System not capable of selected features
  • X.3.4 - Message too big for system
  • X.3.5 - System incorrectly configured

x.4.x Codes

  • X.4.0 - Other or undefined network or routing status
  • X.4.1 - No answer from host
  • X.4.2 - Bad connection
  • X.4.3 - Routing server failure
  • X.4.4 - Unable to route
  • X.4.5 - Network congestion
  • X.4.6 - Routing loop detected
  • X.4.7 - Delivery time expired

x.5.x Codes

  • X.5.0 - Other or undefined protocol status
  • X.5.1 - Invalid command
  • X.5.2 - Syntax error
  • X.5.3 - Too many recipients
  • X.5.4 - Invalid command arguments
  • X.5.5 - Wrong protocol version

x.6.x Codes

  • X.6.0 - Other or undefined media error
  • X.6.1 - Media not supported
  • X.6.2 - Conversion required and prohibited
  • X.6.3 - Conversion required but not supported
  • X.6.4 - Conversion with loss performed
  • X.6.5 - Conversion failed

x.7.x Codes

  • X.7.0 - Other or undefined security status
  • X.7.1 - Delivery not authorized, message refused
  • X.7.2 - Mailing list expansion prohibited
  • X.7.3 - Security conversion required but not possible
  • X.7.4 - Security features not supported
  • X.7.5 - Cryptographic failure
  • X.7.6 - Cryptographic algorithm not supported
  • X.7.7 - Message integrity failure
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n/a Points
2018-03-05 8:44 am

i got this error code [SMTP protocol failure: syntax error: 3-digit code not found; ] simentanuosly durring mailling what kind of error this is and how can i  rectify this error 

1,173 Points
2018-03-05 12:50 pm
If you do not have an error code you will need to contact your hosting provider so they can review the mail server logs to see whats going on.
n/a Points
2017-11-28 10:59 pm

Each of the following recipients was rejected by a remote mail server.

The reasons given by the server are included to help you determine why
each recipient was rejected.
554 dnvrco-cmimta15 esmtp ESMTP server not available AUP#I-1000
Please reply to <>
if you feel this message to be in error.
31,313 Points
2017-11-29 9:56 am
Since the error states "ESMTP server not available" this indicates a delivery failure. If you are seeing this message "from remote mail server after RCPT" then it is an issue with the recipient server. You can also review your mail logs to determine if the delivery is successful. If it was not delivered, the mail logs will provide additional clues into where in the transaction the failure is occurring.

Thank you,
n/a Points
2017-03-03 1:15 am

Thank you..these details helps me handle SMTP error codes in code.

2,858 Points
2017-03-03 11:27 am
Rajesh, you're most welcome! We're always glad to be of assistance! Have a great day!
42,337 Points
2016-06-10 12:06 pm
Hello Cristian,

I took a close look at the top-level-domain used for the email address ( When I ran a WHOIS , traceroute, or ping, it would not recognize the domain. I even checked at the ICANN ( site and it's not recognized. So, in terms of the issues email delivery, I would start with the domain name first.

If you have any further questions, please let us know.

Kindest regards,
Arnel C.
n/a Points
2016-06-10 11:08 am

good morning , my question is this ; by sending an email to the box throws this mesaje ;



=  Greetings from the MDaemon mail system at  = ============================================================


The following message:


     Session-ID: 923018 (specific to this delivery attempt)

       Queue-ID: pd50002228004.msg

     Message-ID: 00d101d1c322$4a3b26f0$deb174d0$


could not be delivered to the following recipient(s): (unrecoverable error)


despite one or more unsuccessful attempts to do so.


No further delivery attempts will be made and the message has been removed from the queue.


The original message headers follow at the end of this report.  For information on DSN messages see


Please quote the Queue-ID, Session-ID, and Message-ID found above in any inquiries regarding this message.



=  Session Transcript  =



  Session 923018; child 0002

  Parsing message <xxxxxxxxxxxxxxxxxx\pd50002228004.msg>

  *  From:

  *  To:

  *  Subject: test

  *  Size (bytes): 1277

  *  Message-ID: <00d101d1c322$4a3b26f0$deb174d0$>

  Resolving MX record for (DNS Server:

  *  P=010 S=000 TTL=(1282) MX=[]

  Attempting SMTP connection to

  Resolving A record for (DNS Server:

  * TTL=(53) A=[]

  Attempting SMTP connection to

  Waiting for socket connection...

  *  Connection established -->

  Waiting for protocol to start...

  <-- 554 cmsmtp ESMTP server not available

  --> QUIT



=    End Transcript    =


can you help me with this problem please?

greetings from Argentina.



n/a Points
2015-10-21 3:47 pm

Hi My name is himanshu.

please suggest me , my lan users are not able to send the mail,it shows in outbox, error says check with your ISP


But Lan users are able to send mails when i am changing the LAN public ip



42,337 Points
2015-10-21 8:19 pm
Hello Himanshu,

Sorry for the problem with your outbound mail. If you are maintaining the IP address and email server for your installation, then I would highly recommend reviewing the bounce messages when your emails fail. These bounce- messages will give you the specific information you require to see WHY an emails. If it is failing due to a blacklist, then it will be indicated in the bounce along with the information on who to contact in order to be de-listed. This is what appears to be happening based on the fact that you're changing public IP addresses and then your mail starts working again. Please check out our article: Why do email servers get blacklisted.

I hope this helps to answer your question, please let us know if you require any further assistance.

Arnel C.
n/a Points
2015-10-22 3:22 am


Thanks for responce.

Somebody suggested me to do create PTR, will it help

31,313 Points
2015-10-22 10:35 am
Hello himanshu,

Thank you for contacting us. Yes, creating SPF records with PTR can often help your email get delivered.

But keep in mind there are many reasons email may not be delivered, so it must be handled on a case-by-case basis.

Reveiwing your servers mail logs is the best method for troubleshooting most email issues.

Thank you,
n/a Points
2015-10-15 1:08 pm

Looking for some help with Server error: '452 too many recipients'. the list above says this is an system storage issue. I was able to send to the list before. Suggestion help.. thanks in advance

10,077 Points
2015-10-15 3:13 pm
Hello Rich,

How many emails are you trying to send out at one time? Most servers have hard limits, ours are set to 50.

Best Regards,
TJ Edens
n/a Points
2015-10-19 9:30 am

One of my clients experiencing the same issue, was trying to send out an email to 130 recipients. is there a way of resolving this, maybe increase the limit?

43,761 Points
2015-10-19 5:38 pm
Hello Mildred,

Our shared servers are hard set to only allow 50 recipients per email. This is not a setting that can be changed at the account level.

Kindest Regards,
Scott M
n/a Points
2015-07-03 12:49 pm

site 2 weeks I cann't send with smtp service of yahoo, error 200 "unknow error certificate bad; destination host name does not match in certificate, even if I use different PC

43,761 Points
2015-07-06 3:40 pm
Hello Grillo,

If you are one of our customers you will want to contact Live Support for account specific help.

Kindest Regards,
Scott M
n/a Points
2014-12-15 2:33 am

404 not found, its clear explanation, can't access the webmail login page


43,761 Points
2014-12-15 12:09 pm
Hello Swetha,

404 is not an SMTP error but a server error when it cannot find a page. Are you getting this error when trying to log in? If so, what is the URL you are trying to log into?

Kindest Regards,
Scott M
n/a Points
2014-03-22 10:14 am

Thank you. The listing helps me explain better to users.

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