For any email marketing campaign, what happens after the send is, obviously, important to understanding the performance of your strategy.

But not every email gets through. And that’s what we’re going to be talking about: email bounce backs.

An email bounce is the Internet’s version of getting a letter in your physical mailbox labeled “return to sender.” In the broadest terms, it means your email was unable to be delivered for one reason or another.

There are two common types of bounced emails: hard bounces and soft bounces. Generally, a hard bounce means a permanent error, or that the email isn’t good for the foreseeable future. A soft bounce means a temporary error and sometimes a soft bounce can be fixed and those emails can be used again in future campaigns.

Let’s get into a little more detail.

What Is a Hard Bounce?

Hard bounces are a permanent bounce or error. This means that the email cannot be received by that address for whatever reason.

Hard bounces can come in many forms, but typically they are the result of user errors such as:

  • The email address simply doesn’t exist
  • The address has been deactivated (typically when an employee leaves a company)
  • The email address has a typo which makes it invalid (e.g. typing @yhaoo.com instead of @yahoo.com)

Photo Source: mailup.com Other reasons an email can hard bounce are that the domain name no longer or never existed, or the recipient has blocked all further emails from you.

However, valid email addresses can also hard bounce due to a variety of reasons such as:

  • Being Denied by Firewall or Filter

Sometimes an email can hard bounce due to a spam filter that interpreted your campaign content as spam. Spam filters reside on either the recipient’s computer or a company’s email-server firewall.

Common SMTP replies for emails marked as spam are “Denied, Unacceptable Content, Blocked, or something similar.”

If you know the person whose email address hard bounced, try sending a regular email with a simple “How are you doing” message. If that goes through, the issue lies within your email campaign or the campaign’s content.

  • Blocked by Your ISP

These types of blocks are typically temporary after spam complaints subside, but it is possible for a large ISP, like Gmail, to block your emails.

Managing your email list’s hard bounces is a critical step to your email marketing campaign. As a general rule, if you know for sure a hard bounce is due to one of the user errors listed above, it’s best practice to remove those addresses from your list immediately and place them in a separate list so that you never accidentally send emails to those addresses again.


What is a Soft Bounce?

Soft bounces are temporary bounces that typically can be successfully sent at a later date.

Emails could be soft-bounced because:

  • The recipient’s mailbox is full
  • The email account was suspended temporarily
  • The recipient’s email server is down due to an unexpected error
  • For whatever reason, you’ve been blocked by the recipient’s email server due to too many of your emails being marked as spam
  • Your domain is on a blacklist
  • Your message is too large

Some soft bounces don’t need immediate attention because they sometimes resolve themselves on their own.

However, they should be closely monitored. If after three bounces the issue doesn’t resolve, further steps should be taken and the address should be treated as a hard bounce.

What to Do with All Those Email Bounces?

Whether it’s a hard bounce or a soft bounce, it’s time to clean your email list. If you repeatedly send emails to addresses that bounce, ISPs will start to think you have bad email practices and can place you on a more permanent blacklist.

We recommend you look at your bounce stats once per week and clean up what you can. If you’re in the midst of a particularly large campaign, you may want to check more often.

If you have clean lists and you’re following email campaign best practices, your sender reputation can dramatically increase (or decrease if you don’t).


If you’re active in managing your list’s integrity, you’re more likely to be sent to people who actually want to engage with you.

Using an Email Validation Service

To help reduce the number of bounce backs using an Email Validation Service, like Email Oversight’s, can help reduce-to-eliminate sending emails to addresses that will bounce.

Syntax errors, abandoned accounts, and all the other reasons that an email list gets filled with invalid addresses can be prevented with real-time email verification.

This happens when you add an email validation service’s API with that of your Email Service Provider (ESP). At that time, opt-in forms on your site are immediately screened for validation, syntax, STMP, and double opt-in confirmation emails. Not only will an email validation service reduce bounce rates in your campaign, but other benefits include:

  • Improve click-through rate
  • Increase open rates
  • Reduce the cost of sending email campaigns
  • Save you the time of cleaning your list manually
  • Better identify potential leads and segment customers.

To inquire about an email verification service, please contact us today.

Hopefully, you now have a better understanding of the differences between a hard and soft bounce in your email campaign. With the tools described in this article, your email campaigns and sender reputation will never be better!

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