Soft Bounce vs. Hard Bounce: What is It & Why Emails Bounce

Soft Bounce vs. Hard Bounce: What is It & Why Emails Bounce


Shortly after you’ve hit the ‘Send’ button on your outreach campaign, the first responses start flowing in. More often than not, though, these are not precisely the replies you were hoping for. Quite opposite - these are notifications about failed deliveries commonly known as email bounces.

Not all bounces are equal and not all are to be overly concerned with. Some, though, can be pretty nasty and can seriously harm your email deliverability. For that reason, it’s definitely worth getting yourself familiar with different types of email bounces and common ways of addressing them.

1. What is an email bounce?
2. What is a hard bounce?
3. What is a soft bounce?
4. What is an acceptable email bounce rate?
5. How to improve your bounce rate?

What is an email bounce?

Every time an email bounces, you’ll get a quick response to your message. Here’s a Gmail example of such an autoresponder:

Email bounce


These messages tend to be quite descriptive. They may return some cryptic error codes (500 5.1.1 here) but almost always will follow with a more human-friendly description of a problem.

Mail Delivery Subsystem may reach out to a sender for many other reasons too. Sometimes they’ll also describe the next steps, as was the case here:

Email bounce message with next steps

To understand what is an email bounce, let’s look at two possible outcomes of a failed delivery - a hard bounce and a soft bounce.

Hard bounces indicate a permanent failure of email delivery. Typically they’re a result of sending an email to a non-existent address or one that won’t accept any incoming mail.

At times, email service providers (ESP) may also reject your emails because they suspect you of being a spammer or other type of fraudster. Every time that happens, a hard bounce will be recorded on your account.

Soft bounces are, well, softer by nature. They indicate a temporary problem with your delivery - a recipient’s server declining your message or an inbox so full that it can’t accept any more emails. It could be an email server timeout, a message too heavy to be accepted, or virtually any other error that, in theory, can be fixed.

For that reason, ESPs tend to retry the delivery of such emails, hoping for a more positive outcome on the following attempts. Only if they fail multiple times (for example, an inbox is still full on the third or fourth consecutive attempt), a soft bounce will convert into a hard bounce and no further efforts will be made.


What is a hard bounce?

As I mentioned earlier, hard bounces are nothing else than a permanent failure behind an email delivery. You’ve had one shot, it failed, no further attempts will be made.

There can be several reasons for hard bounces:

  • The recipient’s email address no longer exists (or never have in the first place)
  • Your email was marked as spam and declined
  • The recipient’s server doesn’t accept any emails or accepts only those from pre-approved users or domains (common practice on governmental or institutional domains)

Hard bounces happen often when you’re cold-emailing. You probably scan a lot of websites, hoping to find the emails of potential leads to your spreadsheet. You may get a hold of a dated email list or manually type in an address, wishing that it belongs to that decision-maker you’ve long had in mind.

More often than not, you’ll be right. But, at times, you'll stumble upon invalid email addresses that will hard bounce. Each time, a record of each bounce will be stored in the network. The more often it happens, sadly the harder it will be to deliver future emails.

Removing addresses that bounced from your mailing list is an absolute must. Verifying each email address before sending them any emails is among the best practices for email sending.


What is a soft bounce?

Soft bounce also indicates a failed delivery but one that may eventually succeed. The common reasons for a soft bounce are:

  • Email server timeout or any other connection error
  • Mailbox is full
  • The recipient’s account is temporarily suspended
  • An email is too large
  • A sender is on a blacklist and thus not welcome in an inbox
  • An email failed the recipient’s DMARC policy and was declined

What connects all these reasons is that the next time you send an email, the outcome may be completely different. A full mailbox could be emptied in the meantime and welcome you with all its hospitality. The recipient’s server could work just fine on the next occasion and any issues could have been fixed.

Sometimes, there’s plenty you can do yourself. It could be limiting the size of your message, avoiding spammy words, and making sure you’re out of blacklists.

When a soft bounce happens, you’ll often see an indication of when the next attempt will be made. It would be a good idea to halt any further email sending to this address or even domain until the issues are resolved.

The infographic below should help you understand the difference between both types of bounces.

Soft bounce vs hard bounce

What is an acceptable email bounce rate?

In sales, it’s virtually impossible to avoid bounces.

People change jobs and leave their email addresses behind. Websites and spreadsheets can’t often keep up and the results are failed deliveries.

Typos happen - working with a double opt-in effectively eliminates them but would your leads really opt-in to receive your outreach emails? Unlikely scenario.

Anticipate getting some bounces for each sent campaign but try to keep them to a minimum.

Acceptable bounce rate

Anything around 2% or below is considered a very solid result. That means that for every 100 emails you send, only two or fewer experience either soft or hard bounce.

If you’re scoring 5% or more, that's already a high bounce rate and you've got reasons to worry. If this continues, you may start having trouble delivering even to legitimate contacts.

If you’re at 10% or more, I’d recommend pausing any email sending until you find and address the cause of your problems. If you continue, you’ll find yourself hurting badly your email sender reputation. You also might eventually get blocked by your email sending provider because a high bounce rate affects not just yours but also their reputation.


How to improve your bounce rate?

If your bounce rate is way higher than you would have imagined, it’s time to implement some habits into your routine. They will help you limit the number of bounces and get a more favorable treatment the next time you send outreach emails.

Verify each email address

I talked about it earlier but it’s so important that it’s worth repeating it over and over again. Make it a habit to verify each email address that you plan to send emails too. It will straightaway protect you from many unwanted bounces.

Hunter’s Email Verifier looks up the recipient’s domain and verifies if it’s capable of accepting emails. It checks if the particular address exists on a given domain and compares it against its huge database of professional addresses. If it spots any potential risks, you’ll be the first to know.

It’s really simple to use. On this page just enter the email address you’d like to verify. Press the ‘Verify’ button and wait until it processes. Here’s an example check for the address that failed the verification:

Invalid email address

Email Verifier works for individual addresses but you can also upload them in bulk via Bulk Email Verifier.

What’s more, you can use Hunter’s Google Sheets add-on to automatically verify each new address added to your spreadsheet.

Add the add-on to your Google account and open a spreadsheet with leads. From the top menu, select Add-ons -> Hunter for Sheets -> Open.

An add-on configuration will appear to the right. Select the column where the addresses are stored. Choose to include the verification details if you’d like and press the button.

Hunter for Sheets verification

The email list will be processed and the results will shortly appear.

Hunter for Sheets verification results

Watch out for spam triggers

The copy you write can have a direct impact on whether your message will be delivered, pushed into spam, or soft bounced. There’s a loooong list of words that spammers tend to use but that hardly befit serious senders such as you and me.

This includes all words that push a recipient to make a quick decision (“Buy now”, “Offer won’t last”, “Try it today”). There’s a bunch of phrases that indicate that something is “free” and “risk-free”, that you can “cancel anytime” and “no questions [will be] asked”.

Spammy email
Here’s an example of a pretty spammy email.

If you browse your spam folder, you’ll see plenty of folks that bombard you with “save big time” and “opportunity of a lifetime” kinds of headlines. Promotions folder is filled with “sale”, “discount” and all kinds of “Buy 1, get 1 free”.

These are not necessarily all that bad phrases, seeing how many big brands use them over and over again. But big brands have sent billions of legitimate emails and whether we like it or not, are treated much more favorably.

If you’re not yet as big as Amazon or Walmart, try to use a more sophisticated language. Be less sell-ish / more human in your emails. Learn how to write a professional email and check out our best-performing cold email templates.

Purge your list

A natural consequence of monitoring bounces is purging the list of hopeless contacts.

If someone hard bounces, make sure you never email them again. Treat those soft-bouncing also with caution as some will eventually hard bounce too. Putting a pause on them for a few weeks won’t hurt your results and may give them enough time to sort out the issues.

We don’t recommend buying ready lists as they often contain lots of invalid email addresses that will bounce over and over again. Spend a bit more find finding the leads online and run them via a proper verification process.

If you want to speed things up, use Email Finder to search for already verified addresses from a given domain.

Hunter's Email Finder

Beware especially of spam traps. These are emails accounts set up on purpose by ESPs and distributed across the web. Sending an email to either of them may not result in a bounce but will put you on a public blacklist for a time being. Getting off such a list is tough and takes time so it’s not the experience I would recommend.

Make it easy to opt-out

Let’s face it - not everyone will be interested in what you have to offer. Some users may keep ignoring your emails. Others might be a bit hasty and click on the ‘Report as spam’ button as soon as you send the first follow-up.

Each such report complicates things a bit. A single report won’t do much harm but if it becomes a recurring theme, you’ll find it harder to deliver future emails.

Most people are not mean - they simply want to get rid of you. ;-) And it’s in your interest to make it easier for them.

One of the best practices is to include an opt-out link at the end of each email. You may also include some kind of stop-word procedure into your follow-ups to make it more natural for them.

Email with stop words

If available, monitor also the feedback loops provided by your tool for sending emails. It’s where you’ll find the details of each spam report that was filed against you.

Warm-up your address

IP warm-up process is often recommended to new senders but, in reality, it’s excellent at any stage of a journey.

When you lag behind in terms of bounce rate, the best thing to do is indeed inspecting your list. Often, though, you can’t afford to just stop sending emails for weeks while you’re verifying what’s wrong with your list. The show must go on and your results depend on that.

There’s a bunch of tools for automated email warm-up (like, for example, Warmbox) that sort of fake email sending and generate some really good engagement rates, without actually any effort on your side. It’s not just a complete lack of bounces but also open or reply rates that quickly go up and that’s something that ESPs appreciate a lot.

Focusing just on a bounce rate, let me give you an example. You send campaigns averaging, let’s say 5% bounce rate - a pretty bad result if you ask me. Out of 200 emails sent each week, 10 bounce.

Simultaneously, you start using a warm-up service that sends another 200 emails on your behalf. The bounce rate is 0% and there are some cool engagement stats on top of that.

Overall, you send 400 emails each week and 10 of them bounce. A bounce rate is already 2,5% - still a bit over the edge but a lot more manageable.

I’ve recently wrote a more detailed article on the email warm-up process, be sure to give it a look if you’re interested in exploring the topic.


Final words

An email bounce is never good news. However, understanding why do emails bounce and finding ways to tackle each case is the first step to avoiding many failed deliveries. This, as a result, will help you deliver more in the future, and hopefully, secure more opportunities going forward.

For each campaign, you send, monitor closely the stats behind it. See which emails bounce and check how they made it onto your list. Think if you can improve the process one step at a time.

Irina Maltseva

Irina Maltseva

Head of Marketing at Hunter. I enjoy working on inbound and product marketing strategies. In spare time, I entertain my cat Persie and collect airline miles.

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