An email bounce is an event when the email you send fails to get delivered to the recipient’s mailbox. The email is simply rejected by the recipient’s mail server. Email bounce is classified into two types:

Type of Email Bounce Definition Cause Action Item to Avoid It
Soft Bounce Temporary delivery failure of email
  • Full mailbox
  • Email account suspended, temporarily 
  • Oversize email
  • Server timeout
  • Authentication failed
  • Authenticate your emails
  • Avoid free-sender domains
  • Monitor your email delivery
  • Resend emails
Hard Bounce Permanent delivery failure of email
  • The recipient's address is invalid
  • The receiving server is blocking emails from your domain
  • Clean your list
  • Use the double-opt-in subscription form 

Let’s read on to explore in-depth what is soft bounce in email marketing. We will also see how you can handle these to ensure your emails are actually sent to people’s mailbox.

What is a Soft bounce?

When the email you send fails to get delivered for temporary reasons, it is said to be soft bounced. Temporary reasons mean that if you resend the email, it will probably get delivered.


  • Full mailbox: some people have mailboxes that have limited capacity (it can be self-imposed or maybe by an employer if they are using a work email address). If this limit is reached before you send your email, then your email won’t make it to their inbox. You can resend the email after a day or few days, assuming that the person cleared their mailbox for newer emails to come in.
  • Email account temporarily suspended: If the subscriber has not signed in for more than 365 days, or if their server has detected suspicious activity, their account could be locked temporarily. Which means your email won’t be delivered.
  • Large message size: Some inboxes have filters that restrict the message beyond a certain size. It might be to protect the sharing of some files or data. So make sure that your email doesn’t have any heavy images, GIFs, or attachments.
  • Server timeout: The recipient’s email server may be temporarily unavailable, or undergoing maintenance. If your email is sent during that period, then it will not go through to the receiver’s inbox. For this also, you can try resending your campaign in another few hours or days.
  • Authentication failed: If the receiving server can’t verify your IP or domain, it won’t pass the authentication check and hence your emails will be blocked from being sent to the recipient’s email until you complete these checks.

The action you can take to lower the number of emails that get soft-bounced

  • Authenticate your domain: Domain authentication means that the email received actually came from the sender listed in the ‘from’ field. It ensures that the email wasn’t spoofed by some hacker or it’s not forged. This protects the recipients from spammers, hackers, and scam tactics. So, ensure that your three email authentication standards (SPF, DKIM, DMARC) are being followed by you or your email marketing software.
  • Avoid free sender domains: Whenever you are sending bulk emails, avoid using free services like Gmail or yahoo because or can not be authenticated. It’s always better to use your own domain and email marketing software that can take care of technicalities.
  • Resend emails: You can’t really know about a soft bounce before it happens so you might not be able to prevent it completely. But you can take action after the email has soft-bounced. Simply resend the email after a few hours or after a day.
  • Monitor your email delivery rate: In your email marketing reporting dashboard, monitor the email delivery for each campaign, and take action if you see it go below a benchmark that you can set for yourself. Only when you measure, will you be able to improve it.

SendX takes email delivery seriously and hence automatically tries to resend any soft bounced emails once more. You can also manually see all the soft bounced emails and take action - resend or delete them from the list, permanently.

A healthy bounce rate is below 2%. Anything higher than that will negatively impact your overall email delivery and sender’s reputation. Thus impacting the reach of your email.

Wrap Up

Here's a summary of action items for you to maintain a low soft & hard bounce rate:

  • Clean your email list: Remove the email addresses that have been inactive for more than 6months. It's a signal that these have been abandoned and people are likely to not return there to check any emails.
  • Use double-opt-in: Double opt-in will save you from spammers populating fake email ids in your subscription form. Lesser the number of fake email ids, lesser will be the bounce rate. Hence, more the effectiveness of your emails.
  • Authenticate your domain: Ensure that your three email authentication standards (SPF, DKIM, DMARC) are being followed by you or your email marketing software.
  • Avoid free sender domains: Use your company or brand's domain in your sender email address. Don't use or - these are for personal use.
  • Re-send soft-bounced emails: Re-sending might help reach inboxes which were earlier not reachable or were full.
  • Monitor your email delivery rate: Monitor your email delivery rate using your ESP's data dashboard. If it falls below a benchmark, you should take measures to correct it.

Please note that if your email goes into the spam box of the recipient, it is not considered a bounce. It is considered to be delivered but not just to the inbox. While bounced emails impact your 'delivery rate', an email going to the spam box negatively impacts your ‘deliverability rate’ which is the percentage of emails that go into the inbox and not the spam box.

If you want to read more about it, check out this article on email deliverability.