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Knowledge Base Home aero-right Contacts Delivery aero-right Email Bounces

Email Bounces

Contacts Delivery Updated on February 29, 2024

Email addresses to which email campaigns fail to be delivered are marked as bounces. These email bounces are classified into three categories, soft bounces, hard bounces, and confirmed bounces. Common reasons for bounced emails could be a recipient’s server is temporarily unavailable, the email content was rejected, too many emails were being sent to the inbox, or the email address does not exist.

Hard Bounces

Hard-bounced emails are email addresses that reject email delivery due to permanent failure; one reason could be the recipient’s email address is invalid. Hard-bounced emails will remain in your contact list as active contacts unless they change to a confirmed bounce. We strongly urge you to clean your contact list with our Clean List feature to remove email addresses that previously resulted in a hard bounce.

The following are some code examples given for hard bounces:

  • Mailbox not found
  • Mailbox no longer active
  • Unknown user
  • Incorrect domain
  • In some cases, an email is marked as a hard bounce due to spam filters.

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Soft Bounces

Soft bounces are email addresses that reject email delivery due to short-term issues with the recipient’s inbox. Soft-bounced emails will remain as active contacts in your list. Emails sent to these addresses may experience temporary delivery delays or may permanently bounce. If you are experiencing a high bounce rate, removing soft bounces from your contact list with our Clean List feature can help prevent future hard bounces. Another option is to make a new list of the soft bounces and use a list verification tool to verify they are indeed valid email addresses.

The following are some code examples given for soft bounces:
  • Quota exceeded
  • Too many sessions in a connection
  • Temporary local problem
  • Out of office autoreply

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Confirmed Bounces

Confirmed bounced emails are email addresses that hard bounced on three consecutive email campaigns. All confirmed bounced emails are excluded from your active contact count and will not be emailed if the contact list they are in is selected for an email campaign. If a previously bounced email is opened in another campaign before it has been flagged as a confirmed bounce, that contact’s bounce counter resets to zero. This allows bounced emails to remain in the active contact count instead of being flagged as a confirmed bounce.

Confirmed Bounce contacts are listed separately in your contact list.


The following are some code examples given for confirmed bounces: 

  • 550 No such user (xxx@xxxxxxxxxxxx) Giving up
  • 5.1.1 unknown or illegal alias: xxxx@xxxxx
  • Recipient address rejected: User unknown


If a valid email address is marked as a confirmed bounce, you can manually remove the individual contact from the confirmed bounce list. However, if the contact has been emailed in the last 7 days, the delete option will not be available.

To learn more about our delete restriction, click here. 

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Invalid Emails

Some emails that are considered invalid will not appear as a type of bounce. Instead, they are flagged as invalid emails and added to your Master Invalid List. Invalid emails are undeliverable. To learn more about how we categorize invalid emails, click here. 

To prevent hard bounces, you can utilize a list verification service to detect and remove invalid emails from your list. Benchmark also provides an easy-to-use Clean List feature that removes soft, hard, and confirmed bounces based on the recipient’s history.

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Reasons for valid emails bouncing

Spam Filters

If a spam filter blocks an email on the contact’s end, it could cause it to come back as a hard bounce. This spam filter could be in the company firewall, the ISP/data center, or the contact’s computer.

Email Content

Are there things in your email that would appear to be spam? There are ways to prevent your email from being filtered as spam. Be sure to use the Spam Checker feature in the email editor before sending your email.

Did the email end up in the “Junk” folder?

An email can often land in the contact’s junk folder if a spam filter has blocked it. The more this happens, the higher your odds of being blocked with future emails. To avoid this altogether, you can request that your subscribers add you to their “safe senders” email list. Asking them to add you to their safe sender’s list will help prevent being blocked by filters later and also lower your bounce rate.

ISP Blocking Email

Some ISPs like Gmail, AOL, MSN/Hotmail, or Yahoo can temporarily block email senders and then remove the senders from the blacklist within a day or two. To avoid delivery issues, Benchmark constantly monitors feedback loops to ensure emails are delivered.

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If you have any questions, please contact our support team.