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Email bounces: why they happen & how to fix them

What is an email bounce?

A bounce is a response from a mail server or mailbox provider telling the sender that an email wasn’t delivered. When an email bounces, this means it didn’t make it to the recipient’s inbox. Instead, the mailbox provider returned it to the sender.

What happens when emails are delivered isn’t too dissimilar from what happens when mail is delivered in the real world. Have you ever mailed a package or a letter, but it got returned to you sometime later—maybe it even included a sticker that provided more information on why your item wasn’t delivered? It might be that the address didn’t exist, you didn’t include sufficient postage, or the recipient refused to accept the package.

Picture an email bounce as the digital equivalent of this scenario. Just like a postal service uses stickers and stamps to categorise what went wrong with your letter, a mail server may reject your email with a diagnostic bounce code.

We use this bounce code to work out what happened.

How email bounces impact your sender reputation and deliverability

How bounces are actioned can have a serious impact on email delivery and overall sender reputation.

Bounces can be early indicators of larger problems. These include reputation issues or bad list-building practices (e.g. not getting the correct permissions to send email). If you don’t take them seriously, ISPs will take notice and might block your emails altogether.

Bounce notifications are the mail servers way of giving you a warning and then a chance to correct the behaviours before something worse happens.

We help you by disabling any bouncing emails and flagging that the email address is bouncing. If you were to continue to send emails the mail server may decide to block all your emails, even ones going to legitimate addresses.

Understanding the different types of bounces: hard bounces vs. soft bounces

There are two types of bounces. Soft or hard.

  • Soft bounces occur when there’s a temporary issue preventing your emails from getting delivered.

  • Hard bounces occur when there’s a permanent issue with delivering your email.

We are going to focus on Hard bounces only. These are the types of bounces you need to address. They require action on your part to resolve the issue.

Common hard bounces: What causes them and how to fix them

There are two common types of bounces

1. Domain or email address doesn’t exist

The most common reason for most bounces is that the email address doesn’t exist. While you should take bounces seriously, receiving an occasional hard bounce for invalid emails isn’t unusual. For example, it can easily happen when an email address has a typo.

Resolving “Domain or email address doesn’t exist”

  1. Check the email for typos.

    1.1. Correct the typo and you will be able to send emails to the new email address.

  2. If you think the email address is legit you can check it with an email verification service like . This will tell you information about the email address. For example, if the email address actually exists.
  3. If all else fails contact us at

Sometimes emails can bounce due to their contents. This is usually very rare. This means that your content was rejected by a mail server and can happen for several reasons.

  • are you using any language that might come across as spammy?
  • where are your links going? Are you linking to websites that aren’t secure or that come across as phishy?
  • are you using link shorteners like bit[.]ly? Many mailbox providers find these spammy.
  • rigid corporate policies in place on the receiving mail server

Before a content-related hard bounce happens there will be multiple soft bounces issued by the mail server. These, if no action is taken, will be upgraded to a hard bounce or even a full ISP block.

We watch all outgoing emails and will warn you if we see any content-related soft bounces. Then we will help you take the actions to stop it from escalating further.

We will review any content in the email you have sent and provide feedback on how to fix it.

If we think that the content is good

It will need to be resolved by contacting someone on the receiving mail server side. This will usually be the IT team or mail administration team. They will need to whitelist the sending domain or our email providers sending IP addresses in their mail filter settings.

  1. If comfortable, this can be done by you. It can get a bit technical so we can provide email templates to help give the appropriate information.

    • Sometimes, A follow up by you, the researcher can be more effective than us doing it.
  2. We are happy to follow up on our behalf. Feel free to reach out to us at if you want us to handle it.

Feel free to get in touch if you have any content-related concerns or questions.

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