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
2014-03-22 10:14 am

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

n/a Points
2014-12-15 2:33 am

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


23,321 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

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