Why do emails bounce and how to avoid it

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Your prospects won’t see the personalized messages if you don’t hit their inbox. 

An important metric to consider when launching email outreach is bounce rate. Particularly if your industry has a limited market or you are planning mass mailing.

It is painstaking for your sales team to succeed if you don’t handle email bounces properly. It isn’t your sales representative’s responsibility to know all the technical nuances about their cold campaigns. 

What does bounced email mean

Email bounce means that your message cannot make it to your lead's inbox. That’s why you receive an auto-email about a failed delivery. The notification contains explanations for why the email doesn’t reach the recipient. A common reason is that right before sending you skip rechecking the validity of the email contacts. Example.            


If you receive «email was not delivered» message, go through what the email vendor advises on this, so you can do something about such messages before it harms your company. 

Why do emails bounce

Bouncing emails is the result of rejecting emails of the recipient's mail server. 

What does it mean to bounce a server? The server does it for numerous grounds:

  • you (sender) — forgot to validate contacts before the outreach, have credibility issues, improperly authenticate the account, etc. 

  • recipient — accept only pre-approved users, their server experiences technical problems, their mailbox lacks cloud space, etc.

Hard vs. soft bounced email

A hard bounce indicates a pressing problem that requires to be fixed before sending the message again. You can identify the type of bounce by checking the server response, typically below the ESP message — it starts with 5.X.X. A soft bounce means a minor issue, and after some time has passed, you can resend the same email. In this case, the server message will start with 4.X.X

There are two types of bounces so that you can quickly assess how serious the problem is

What is a hard bounce

A hard bounce (HB) means resending the message won’t change the outcome while harming your reputation. You require to sort out the issue first. We’ll suggest the solutions in the article. Typical hard bounce reasons: 

  • an unverified email contacts

  • you didn’t make DKIM, STF, and DMARC records properly

  • you got several reputation soft bounces and didn’t fix the problem 

  • you are suspected of spam activities

Normally ESPs don’t let you resend the HB email and turn it into a suspended email address.

What is a hard bounce in email marketing

Such hard bounces are auto emails explaining your newsletter didn’t reach some subscribers. It happens because of a constant issue with the recipient's or your account. Most email services automatically remove hard bounced recipients from your database when the problem occurs. Yet, be attentive to HBs.

What is a soft email bounce

A soft bounce (SB) means there are short-term problems preventing your message to be delivered. Often it isn’t you, it is the recipient. ESPs usually attempt to resend the email automatically, presuming the issue is resolved. One-off SBs occasionally aren’t harmful. Yet, if you get them repeatedly, they may change to hard bounces and affect your reputation.

The aftermath of email bouncing

Why does email bounce back

You can uncover the reason for this email bouncing in your email campaign analytics. Here is how it looks in Postmark. 


Clicking on each bounce group and each not delivered email allows you to learn reasons in depth. 

Below are the most expected types of hard and soft bounces and what to do with them.

1. Hard bounce: invalid email address

  • the account was deleted

  • you or your recipient made a typo 

  • the recipient intentionally made the email address fake

  • you used an accept-all email from the verification tool

  • the recipient account doesn’t welcome any emails or only selected domains and accounts

  • you are under the recipient’ block 

Get rid of such contacts from your list. Usually, email vendors do it automatically. By keeping the address and attempting to send it repeatedly, you run the risk of being blacklisted. So you will be able to send nothing. 

Note: If you have a limited target market — try to discover the correct contacts of the leads or request permission to contact them. 

2. Hard bounce: improper authentication

Hard bounce email also occurs because something is not correctly set up. You should go through your DKIM, STF, and DMARC records. The emails are blocked by Gmail this way:

3. Soft bounce: the mailbox ran out of memory space

In this case, your recipient cannot get any emails. Assumptively, the email account is old and isn’t used anymore. So just take them off your contact list. 

If they are valuable leads — try to resend in a month, or even better — locate other contacts of the person. 

4. Out-of-office or autoresponder

Often such messages notify you the recipient is on holiday or that the person quit the organization. They are sometimes treated as one of the reasons emails bounce, though in this case, your email will reach the lead’s inbox

It is a wise decision to review autoresponders — you will know when to follow up or that there is another person to contact.

5. Soft bounce: server overload

If you are used to sending emails in prime times, you might face SBs because of large traffic. The recipient’s server may also be under maintenance or experience technical issues. 

In this situation, resend the email later.

6. Soft bounce: email size

Email bouncing may happen if the attachments are too large. For instance, for Gmail, your email should be up to 25 MB. Besides bounces, heavy emails might end up with a technical error, so recheck what the «sent» email looks like. 

To fix it — place your files in the cloud. 

7. Sender’s reputation

Both SB and (then) HB may happen because of the sender's reputation — account, domain, or IP. Reputation bounce comes from spam complaints, the spammy content, dramatic surge in your mailing list size.

Using some email providers, you share IP with several other accounts and might be punished by chance. As a result of a bad reputation, you might be blocklisted. Game over. 

You can uncover details in our previous blog article about deliverability. 

8. Long email text (kidding)

You won’t get bounced for a long text, though it is better to keep it short :)

How to reduce email bounce rate

Now, let’s dive into how to prevent high bounce values and how to keep it under acceptable limits.

  • Always verify emails just before a campaign. The validity status may change if you found the emails a week or a month ago. To be even more sure, test the email on your additional email account. Email verifiers won’t provide you with a 100% guarantee that a valid email won’t bounce. For instance, GetProspect can ensure that 95% of valid emails won’t bounce. If the value is lower, contact our support team.
  • Be wary with accept-all emails. «Accept-all»/«catch-all» emails cannot be verified by any service. They might be valid or invalid. In the GetProspect tool, they are labeled with a small orange circle.
    Sending to accept-all emails (only them) might result in up to a 25% bounce rate.

    If you choose to mail to accept-alls, we recommend sending in small batches and also conducting an email bounce check with an alternative email address. That way, if they bounce, they won’t hurt your main account’s reputation.

  • Employ more accounts. Vendors usually set a limit of 100-250 emails a day per acc. To be 100% sure of safety, our sales send up to 50 emails each.

  • Watch out for bounce rate and changes. The less you check email bounces, the higher the bounce value you’ll have because you don’t fix the triggers of the bounces. Most mailing tools provide the analytics of sent, bounced, opened, clicked, complaints, unsubscriptions, etc. It is especially critical to track for bulk campaigns and industries with a limited market.
    If your email vendor doesn’t deliver the data, determine the average bounce rate for the email outreach yourself: (№ of bounces / № of delivered emails)*100.

    Every email provider sets an acceptable bounce rate for its users’ email campaigns to protect its domain. For instance, MailerLite mentions it in its Anti-spam policy: The ideal bounce rate is under 2%. For cold mails, the «OK» bounce rate could be as high as 10%. They are more susceptible to bounces since people don’t agree to receive the mails.

    Be wary of looking at just the overall number of bounces: impulsive surges of bounce value may be a sign of a problem too — and if you catch them early, you can resolve them before they cause further damage.

  • Pay attention to bounce types and prioritize. Sort out reputation-related HBs first — they have a more serious negative impact. Second, fix SB caused by spam content and complaints. Third, sort out other HBs.

  • Launch a mailing campaign only when you set technical things properly. To be sure, consult technical delivery experts, or even hire one if you have a lot of mailing campaigns. 


  • If you skip email bounces, your sender’s reputation is at stake and you might be blocked by your mailing tool or blocklisted. 

  • Email bounce back as because you did something wrong as because of the recipient’s issues. You need to watch both bounce types. 

  • To decrease bounce value validate the mailing list right before the campaign and track bounces.

  • The median bounce percentage across companies is 4.31%, though better keep it under 2%.

  • You’ll still have bounces even if you are doing everything correctly. Your goal is to keep it under the minimum level. 

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