What is a hard bounced email?

Email marketing campaigns rely on emails getting through to their intended recipients. When they don’t, it’s a big problem for the performance of your campaign. Plus, there’s a risk that that it’ll negatively impact your sender reputation, reducing deliverability and engagement further in the future.

The trick here is to avoid dreaded hard bounces in the first place, but how? 

That’s the question we answer in this post. You’ll learn what a hard bounce is, how it differs from a soft bounce, and how you can check if a hard bounce occurred. You’ll also find out about the effect that it might have on your sender reputation and how it might affect your email deliverability in the future. Read on to learn more:

Hard bounces vs. soft bounces

The difference between a hard bounce and a soft bounce is more critical than many senders think. While both result in the same primary outcome – your message not getting through – the secondary consequences are different. 

A hard bounce is where an email doesn’t get through to your recipient because of a “permanent failure”. Permanent failures are things that are unlikely to change and can be for reasons such as…

  • An invalid domain name
  • An invalid mailbox (or one that’s been closed down)
  • A disabled recipient email address

Soft bounces are different. Usually, these are temporary or reputational issues which may either resolves themselves over time or you can take steps to fix them yourself (such as domain or IP blacklisting). Here are a few common reasons why emails soft bounce…

  • Email server is down, perhaps due to a hack or outage
  • Email service is running slow or timing out
  • Mailbox is full
  • Failure of the message to pass DMARC, DKIM and SPF authentication checks
  • Mailbox providers thinks the email is Spam
  • Mail server has some configuration issues

How you’ll know when emails hard bounce

Most emails that hard bounce happen while your ESP is talking to the destination mail server and all of that happens as part of the SMTP conversation. Some emails get accepted and are then bounced later in what’s called an Asynchronous Bounce.

In both cases though, there will always be more information about the reason why the email has been rejected and that information can be used to clean-up your list by removing invalid email addresses – a big win for your sender reputation.

Many email service providers will send you A Delivery Status Notification (DSN), telling you that there was a permanent reason they couldn’t deliver your email and typically you’ll see codes and messages like these…

  • Code 500: The recipient’s email address does not exist
  • Code 511: Bad destination mailbox address
  • Code 514: Mailbox destination address is ambiguous
  • Code 518: There’s something wrong with your email address
  • Code 523: The message exceeds the administrative length limit
  • Code 532: System does not accept network messages
  • Code 541: No message from the host
  • Code 552: Syntax error
  • Code 551: Invalid command
  • Code 571: Delivery not authorized or refused
  • Code 572: The email recipient’s email hosting service does not support your security features

What effect does a hard bounce have on your sender reputation? 

Internet service providers and mailbox service providers track senders and by doing that it determines your “sender reputation”. 

When sender reputation is good it means that you are trusted and as a result, less emails will be rejected, more emails will land in the inbox as opposed to the junk folder meaning engagement will be higher. When sender reputation hasn’t been established (because you’re a new sender) or it’s bad the result will be the complete opposite and you’ll see increased numbers of emails being rejected and lots of emails filtered into the junk folder.

Hard bounces can negatively impact your sender reputation. It’s one of several signals that are used for determining sender reputation so staying on top of domain and IP health checks, list hygiene and best practise are key.

Here are just a few things that you can easily do… 

  • Once you know an email address has hard bounced, remove it from your list
  • Ensure that your sending domain has DKIM, SPF and DMARC records
  • Monitor domain and IP address blacklists
  • Make sure you’re handling Feedback Loop Complaints

How to prevent hard bounces

Naturally, the best solution is to prevent hard bounces from occurring in the first place. While it’s unlikely that you’ll ever get the number all the way down to zero, you should be able to get it under the 2 percent threshold with the right approach. 

Use double opt-in

This approach is pretty common and it is a really neat way of ensuring the email address people sign-up with is accurate.

It’s a two-step method where people do not get opted in until they’ve clicked the link in the email you send them to confirm their email address.

It’s a sure fire way to reduce the number of hard bounced emails.

Use an email verification service

The number one reason for hard bounces is that the email address no longer exists, or exists in a form that renders it uncontactable (perhaps because the service that used to host it is no longer operational). 

Instead of testing to see whether the email exists yourself (by sending a campaign), it’s a much better idea to use you may want to use an email verification service that won’t affect your sender reputation. 

Email verification can be useful if you’re using a list that hasn’t been sent to for a while as it’ll reduce the risk of higher numbers of hard bounced emails. These type of services aren’t 100% accurate though as the method for checking whether a mailbox exists without sending an email to it isn’t supported across all ISPs and email services.  

Offer easy-to-spot unsubscribe options

People change their mind and if they signed up last week but don’t want your emails today then you should respect that.

Making it easy for people to stay “stop” is not only required by law but it’s also good for your brand and that person might come back in the future because their last experience was a good one. 

Protect your forms and landing pages using reCaptcha

Any web pages that capture email addresses are open to abuse from bots and that is a real pain for email marketers.

Google’s reCaptcha is a good way of protecting websites from abuse and will help to stop email addresses of people that did not sign-up from ending up on your lists.

Wrapping up

In summary, hard bounces can seriously affect your sender reputation but the good news is that you can take simple steps to prevent that from happening.

It’s also critical that you comply with the GDPR (or any other legislation applicable to you and your recipients) to ensure that you have a lawful basis for sending people emails – such as “opt-in”. Plus, make it easy for recipients to click unsubscribe at any time if they change their mind. 

One hard bounced email won’t destroy your sender reputation but repeatedly sending to email addresses that are known to be bad will so give yourself the best possible chance of campaign success by staying on top of list hygiene and email marketing best practice.

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