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How It Works Video GDPR Blog Case Studies Managed Campaigns For Small Business Free Marketing Plan
Why Email Works Open Account Building Lists Email Marketing What Are Bounces?
Contact About Us Meet The Team UK Based Reviews

understanding bounces

what are hard bounces and soft bounces?

When an email cannot be delivered to it’s intended recipient, this is called a bounce. In a nutshell, the email was bounced back to you (the sender), as it could not be delivered to it’s final destination.

Bounce types; quick navigation

What is an email bounce?

There are a vast array of reasons why an email may bounce; ranging from the recipient’s email server experiencing technical issues, through to a simple typo when entering the subscriber’s email address.

Bounced emails are categorised into one of two categories; a Hard Bounce or a Soft Bounce. Understanding the difference between bounce types provides an insight into why the email send failed - and if we retry sending, will the email be delivered on a second attempt?

What is a Hard Bounce?

A hard email marketing bounce is normally defined as a permanent error. This is an error that is not likely to be resolved if you retry sending the email at a later date.

A common example could be that the recipient’s email server does not exist. This could be caused buy a misspelling when entering the email address or perhaps the recipient’s company is no longer trading, as a result their email server has been shut down.

At email blaster, all hard bounces will be auto removed from your mailing lists within 7 days. The email blaster cloud runs a full sweep of your mailing lists every Friday, removing all identified Hard Bounces.

When importing any new mailing list into your email blaster, as part of the List Ai analysis, the platform is able to detect and remove Hard Bounces prior to using the email list. This helps protect your sender score by removing invalid data before sending a single email.

What is a Soft Bounce?

A Soft Bounce can be identified as a temporary error. This is an error that may be automatically resolved by the time of sending your next email marketing campaign.

A common example could be that the subscriber’s inbox was full at the time of sending your email marketing campaign. As a result, there recipient had no available space to store your incoming email, so it was rejected. In normal situations it is assumed that the recipient may free up some inbox space before sending your next email.

As a Soft Bounce is normally a temporary issue, email blaster will only remove after two or more consecutive occurrences. In this scenario it is assumed that the error with your recipient’s email server is not likely to be resolved. The email address is then tagged for removal and removed within 7 days (as part of the previously described weekly audit).

Understanding your email marketing bounces.

To help understand the exact reason why your email marketing bounced, recipient servers will respond with an RFC code. According to RFC standards, Hard Bounces are depicted by a 5XX response code and soft bounces with a 4XX response code.

Not all email service providers (ESP’s) respond with valid RFC codes, this can sometimes lead to inconsistencies when it comes to correctly categorising the exact reason why your email marketing send bounced.

To help overcome inconsistencies, email blaster has developed a learning bounce management platform that reads bounce codes; aiming to correctly categorise every bounce into easily to understand definitions:

421

Suspected mail bomb (Soft Bounce)

Recipient servers often run an email marketing rate limit, capping the amount of emails that you can send to their network per hour. The limit will vary between email service providers, your external sender reputation is also taken into account by ESP’s.

If you have built up a positive sending reputation (through good levels of engagement and minimal spam reports), this often results in a higher rate limit being available to you. This means that you can send more emails to the same domain name per hour.

If you notice that your analytics bounce report contains ‘suspected mail bomb’, this means that the recipient email service provider has deemed that your mailing list contains too many email addresses at the same domain (and your list exceeds the allowed hourly rate limit for the ESP in question). After reaching the limit, the recipient service provider will reject further incoming messages until the hourly rate limit expires.

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450

Mailbox temporarily unavailable (Soft Bounce)

The recipient’s email server reported that it was temporarily unavailable. In most cases this is caused by a network error with the recipient’s server.

There may have been an internal routing issue with the receiving mail server which resulted in it being unable to deliver your incoming email to the end users mailbox.

In most situations it is expected that the users network administrator will resolve the issue by the time of your next send, email blaster will class this as a Soft Bounce.

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451

Error with subscribers mailbox (Soft Bounce)

When receiving your email, the subscriber’s mailbox reported an undisclosed internal error during transmission of your message.

This may have been caused by a misconfiguration with the subscriber’s mailbox (or mail server). It was unable to recognise a command issued by email blaster during transfer of your message.

This is normally classed as a temporary issue. In most cases you can expect any outstanding issues to be resolved by the time of your next email marketing send.

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550

Recipient rejected message (Soft Bounce)

The recipient email server reported that it was not able to accept your incoming email.

Receiving servers will analyse your incoming message taking a look at: images, content text, send from settings and your subject line. The recipient server reported that your email may have looked like spam.

To resolve, it is recommended that you check the following areas:

  • Verify your domain. Ensure that you have verified your send from domain name with email blaster. This allows us to add DKIM and SPF authentication to your mailer. Adding authentication will have a large positive impact on your open and delivery rate.
  • Check spam score. Before sending your next campaign, analyse it with the email blaster spam score app. This will help identify any issues with the content that may impact delivery.
  • Avoid 3rd party lists. ESP’s often reject users using 3rd party lists due to spam reports.
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551

Mailbox does not exist (Hard Bounce)

The recipient email service provider reported that it was not able to accept your email. The mailbox may no longer exist and has been shut down, or there may be a issue with the incoming mail that caused delivery to fail.

If a mailbox no longer exists, Email blaster will classify this as a Hard Bounce and remove the subscriber within 7 days.

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552

User’s mailbox is full (Soft Bounce)

Most users have a storage limit on the amount of emails that they can store. The recipient email server reported that your subscriber’s mailbox was full. When a user’s mailbox is full, the recipient server will reject all incoming email until the user has made additional storage space available.

In most cases it is expected that the subscriber will free up additional mailbox space by the time of your next send, therefore email blaster will class this as a Soft Bounce.

In rare cases, the user may have stopped using or abandoned their mailbox, in this scenario after multiple consecutive occurrences email blaster will class this as a Hard Bounce and tag the user for removal.

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554

Mailbox unable to accept mail (Soft Bounce)

The subscriber’s email server reported a non-standard reply that was not recognised by email blaster. This may have been the result of a misconfiguration with the recipient’s email server or data becoming corrupted when reaching the recipient server.

It is assumed that this is a temporary issue that may be resolved by your next campaign send. Email blaster will classify this as a Soft Bounce.

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517

Error with your send from address (Soft Bounce)

Recipient email server reported an issue with your send from settings. ESP’s will often validate your send from email address - checking it for typos and that it is ultimately a valid email address that is capable to receiving email.

It is recommended that you review your send from settings, the recipient server reported that they were invalid - check for any misspellings or missing letters.

Email blaster will classify this as a Soft Bounce - it is expected that you will resolve any issues with your send from settings before the next campaign send.

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541

Subscriber’s server too busy (Soft Bounce)

Your email could not be delivered, the subscriber’s server either did not respond or was too slow to respond. This can occur if the recipient email server is very busy or experiencing technical difficulties.

Email blaster will normally retry over a few hours, however this initial bounce report will still be reported inside your analytics even the next delivery attempt was successful.

This is normally a temporary issue with the recipient server that may be fixed by your next email send. Email blaster will class this as a Soft Bounce.

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542

Subscriber's domain does not exist (Hard Bounce)

Defined as a Hard Bounce, the subscribers domain name/email server does not exist. The domain name is the part after the ‘@‘ symbol inside an email address.

This could have been caused by a misspelling when entering the users email address, or the organisation you are trying to reach does not exist.

Email blaster will automatically tag this subscriber for removal, retrying a send is likely to fail.

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523

Message / send from settings issue (Soft Bounce)

There was a problem with the content of your email or send from settings, this caused delivery to fail. This bounce can be caused by one of multiple reasons.

To resolve, it is recommended that you run your campaign through the email blaster spam score check. This will help identify any issues with the content.

You should also check that your send from domain has been verified with email blaster (via the sender profiles screen), this allows email blaster to add additional authentication to your campaign for improved delivery.

In some rare cases, recipient servers will not allow very long messages. While in most cases unlikely, check that your email newsletter is not too long and contains neat HTML coding.

Email blaster will class this as a Soft Bounce. It is expected that any issues with your message or send from settings will be resolved by your next campaign send.

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400

Temporarily deferred (Soft Bounce)

Your message was temporarily deferred by the recipient email server. In this scenario the recipient server will initially reject your message, asking email blaster to try again at a later date. Email blaster will auto re-try delivery after a set period of time. Subscriber’s shown inside this category may have been successfully delivered on 2nd attempt.

Some services such as Yahoo will defer messages if you have had previous history of spam reports. Alternatively if you have not sent to this subscriber before, the recipient may use ‘grey listing’ for new senders, this initially rejects the message asking email blaster to try again in he few hours.

This is classed as a Soft Bounce, issues related to this failure may be resolved by your next campaign send.

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575

Send from domain not authenticated (Soft Bounce)

Strict email service providers will ask that your send from domain includes DKIM and SPF authentication. Both authentication methods are automatically added when verifying your domain with email blaster (via the sender profiles screen). It appears that you have not yet authenticated your domain name with email blaster.

Taking the time to verify your domain will boost your delivery and open rates. Some email service providers will reject your email without verification being added. Email blaster identifies this as a Soft Bounce, it is expected your next email send to this subscriber will be successful if authentication has been added.

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447

Deferred message, unable to deliver (Soft Bounce)

The receiving email server was unable to accept your message on first attempt, the reason for this was not disclosed - this could be caused by a problem with the incoming message or a technical problem with your subscriber’s server.

In this scenario email blaster will wait a few hours before trying again. On the 2nd delivery attempt, email blaster was still not able to successfully deliver your message.

Double check that your recipient’s email address is correct and contains no misspellings or typos. Also consider phoning your recipient to check that you have their correct email address.

This issue may resolve itself by the time of your next send, this bounce reason is categorised as a soft temporary issue.

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57606

Office 365 rejected (Soft Bounce)

This subscriber is using Office 365 to power their email. Office 365 reported that it was not able to accept your incoming email. This may have been caused by negative history or previous incidents of spam associated with your company.

For further assistance, contact the team at email blaster. We are able to open dialogue with Microsoft to help resolve issues. Please note that if you have received multiple reports of spam, the team at email blaster may not be able to help.

It is recommended that you also have a full audit of your subscriber list to help minimise any future spam reports.

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418

Send from address does not exist (Soft Bounce)

Recipient email servers will often validate your send from address. The recipient server concluded that your send from address was not able to accept replies or incoming email.

To resolve, ensure that your send from address is a valid email address within your organisation. Avoid the use of no-reply@ addresses, in many cases recipient servers will outright reject no-reply@ addresses.

It is expected that any issues with your send from address will be resolved by your next campaign send, email blaster will class this as a Soft Bounce, giving opportunity to resolve your issue.

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569

Routing issue with subscriber (Soft Bounce)

Email blaster experienced issues communicating with your subscriber’s email server. This may have been caused by a network or routing issue at your subscribers email server.

This bounce is defined as a technical issue with the subscribers server. By the time of your next campaign send, it is likely that the remote server has resolved any ongoing issues. Email blaster will tag this as a Soft Bounce.

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5754

Accepts specific user's mail only (Hard Bounce)

Recipient server reported that it only accepts incoming mail from specific users. This email address may be used for internal communications within your subscriber’s organisation, and is not able to accept incoming mail from any external sender.

Consider phoning your subscriber and asking for an alternative contact email address. The current email address is not able to accept incoming mail in it’s current form. This email address will be tagged as a Hard Bounce for removal within 7 days.

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0

Miscellaneous error with recipient server (Soft Bounce)

Subscriber’s email server reported an undisclosed miscellaneous error. The recipient server did not give an exact reason for rejecting the incoming email or a valid RFC bounce code.

Without additional information from the subscribers server, email blaster tags this as a Soft Bounce - as the email send may be successful on next attempt. If the email continues to Soft Bounce after multiple consecutive campaign sends, email blaster will then tag this as a Hard Bounce for removal.

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