What do the different bounce reasons mean :

There are various bounce types that you could find in the report for a sent email. The majority of the bounce messages we get are arranged into delicate bounce classifications or, if it’s a permanent delivery failure, it’s classified as a hard bounce.

Bounce category definitions :

The following categories will not apply to every bounce type out there. We take a simplified approach to bounce message interpretation based on best practices.

General bounce :

This is treated as a soft bounce since we can’t decide the definite explanation behind conveyance disappointment. Ordinarily, this bounce type is related with a specialized issue, for example, “Association coordinated out,” yet we will likewise arrange a bounce as “general” if the reaction from the beneficiary server is available to more than one understanding. It could be a non-standard mistake message, or too obscure to be in any way valuable.

DNS failure :

The beneficiary’s email server is at present unfit to convey your email due to DNS issues on their end. This may or may not be a temporary problem. The error could be because of the mail server is down, or there was a grammatical error when it was set up, or possibly the goal space doesn’t exist.

All we know is that the DNS host is inaccessible, accordingly, we treat this as a delicate bounce to enable some time for the issue to be corrected.

Mailbox full :

The email server can’t convey your email on the grounds that the beneficiary’s inbox is full. Most email applications have a set measure of capacity an individual client can use for email. On the off chance that this standard is surpassed the server won’t let any more mail through, however it will likewise typically alert the letter box proprietor so they can take care of business.

So while the reality of the situation may prove that your beneficiary hasn’t set aside time to make some space, it could likewise be an indication of a relinquished post box. For instance, somebody sets up a free webmail account only for shopping-related messages, at that point quits marking in when they begin putting something aside for a house.

We treat these as a soft bounce in the event that it’s impermanent, however in the event that the issue proceeds with we’ll change over it to a hard bounce for you.

Message too large :

The extent of your email — including all headers, content and pictures — is bigger than the most extreme size the recipient’s mailbox permits. The bounce message returned does exclude data on what as far as possible is, however we advise you don’t send messages greater than 99Kb.

Mail block – relay denied :

Your email has bounced because of a temporary error, which could be on the sending or receiving side. “Relay” just alludes to the transmission of your email from our server to the accepting server, which has in all probability been denied because of client mistake. This kind of bounce for the most part happens when the sender’s message isn’t confirmed, yet it can likewise be expected to a misconfigured server on the beneficiary side.

Mail block – general :

The recipient’s email server is blocking inbound mail from our server, which might be because of blacklisting. A mail block is recorded when the accepting server blocks an email totally; dismissing the message with no endeavor to convey it to the inbox.

The most likely reasons for this block are:
  • Your reply-to address is blacklisted.
  • One of our sending IPs is temporarily blocked.
  • One of our sending domains is temporarily blacklisted.
  • The receiving server only accepts whitelisted senders.
  • Mail block – spam detected :

    The beneficiary’s email server has blocked your email on the premise that the substance looks like spam. This mail block is frequently activated by something identified in your email content, however can likewise be your answer to address or brand name that has a poor reputation. We treat this as a soft bounce because of the way that some mail servers and email suppliers react with false or erroneous mistake codes.

    Transient bounce :

    The recipient mail server can’t deliver your email, but will keep trying for a limited period of time. We treat this as a soft bounce, as when the recipient mail server retries the message could be delivered.

    Challenge/response :

    The recipient has installed software as an anti-spam measure, that just acknowledges email from recently approved senders. On the off chance that the product doesn’t know the sender, a test email is returned, requiring a particular activity before the first email will be sent to the client.

    Bounce – but no email address returned :

    The beneficiary mail server bounced your email, however did not show which address it was skipping in the interest of. We’ve decided the recipient dependent on the substance of the bounce.

    Hard bounce :

    Your email is for all time undeliverable to this email address. The location is either fake, was entered inaccurately, or the client mailbox or domain is no longer active.

    For example, the following are all hard bounce error messages:
  • Unknown or illegal alias
  • Address rejected
  • No such user here
  • Bad destination mailbox address
  • Rule imposed mailbox access for refused: user invalid


  • Standard set of SMTP error codes :
    Traditional Bounce Codes :


    Code

    Type

    Explanation

    421

    SOFT


    <domain> Service not available, closing transmission channel

    450

    SOFT

    Requested mail action not taken: mailbox unavailable (e.g., mailbox busy)

    451

    SOFT


    Requested action aborted: error in processing

    452

    SOFT

    Requested action not taken: insufficient system storage

    500

    HARD

    The server could not recognize the command due to a syntax error.

    501


    A syntax error was encountered in command arguments.

    502

    This command is not implemented.

    503

    The server has encountered a bad sequence of commands.

    504

    A command parameter is not implemented.

    550

    HARD

    User’s mailbox was unavailable (such as not found)

    551

    HARD


    The recipient is not local to the server.

    552

    HARD

    The action was aborted due to exceeded storage allocation.

    553

    SOFT

    The command was aborted because the mailbox name is invalid.

    554

    HARD

    The transaction failed for some unstated reason.


    Enhanced Bounce Codes :




    Code

    Type

    Explanation

    5.0.0

    HARD

    Unknown issue

    5.1.0

    HARD

    Another address status

    5.1.1

    HARD


    Bad destination mailbox address

    5.1.2

    HARD

    Bad destination system address

    5.1.3

    HARD

    Bad destination mailbox address syntax

    5.1.4

    HARD


    Destination mailbox address ambiguous

    5.1.5

    HARD

    Destination mailbox address valid

    5.1.6

    HARD


    Mailbox has moved

    5.1.7

    HARD


    Bad sender’s mailbox address syntax

    5.1.8

    HARD

    Bad sender’s system address

    5.2.0

    SOFT Other or undefined mailbox status

    5.2.1

    SOFT

    Mailbox disabled, not accepting messages

    5.2.2

    SOFT

    Mailbox full

    5.2.3

    HARD

    Message length exceeds administrative limit

    5.2.4

    HARD

    Mailing list expansion problem

    5.3.0

    HARD

    Other or undefined mail system status

    5.3.1

    SOFT

    Mail system full

    5.3.2

    HARD

    System not accepting network messages

    5.3.3

    HARD

    System not capable of selected features

    5.3.4

    HARD

    Message too big for system

    5.4.0

    HARD

    Other or undefined network or routing status

    5.4.1

    HARD

    No answer from host

    5.4.2

    HARD

    Bad connection

    5.4.3

    HARD

    Routing server failure

    5.4.4

    HARD

    Unable to route

    5.4.5

    SOFT

    Network congestion

    5.4.6

    HARD

    Routing loop detected

    5.4.7

    HARD

    Delivery time expired

    5.5.0

    HARD

    Other or undefined protocol status

    5.5.1

    HARD

    Invalid command

    5.5.2

    HARD

    Syntax error

    5.5.3

    SOFT

    Too many recipients

    5.5.4

    HARD

    Invalid command arguments

    5.5.5

    HARD

    Wrong protocol version

    5.6.0

    HARD

    Other or undefined media error

    5.6.1

    HARD

    Media not supported

    5.6.2

    HARD

    Conversion required and prohibited

    5.6.3

    HARD

    Conversion required but not supported

    5.6.4

    HARD

    Conversion with loss performed

    5.6.5

    HARD

    Conversion failed

    5.7.0

    HARD

    Other or undefined security status

    5.7.1

    HARD

    Delivery not authorized, message refused

    5.7.2

    HARD

    Mailing list expansion prohibited

    5.7.3

    HARD

    Security conversion required but not possible

    5.7.4

    HARD

    Security features not supported

    5.7.5

    HARD

    Cryptographic failure

    5.7.6

    HARD

    Cryptographic algorithm not supported

    5.7.7

    HARD

    Message integrity failure