About soft bounces and hard bounces

Article author
Miguel Panayotty
  • Updated

When you send out your campaign, you’ll notice that some emails will return with bounce responses. Learn the difference between soft bounces and hard bounces.


Soft bounces

Soft bounces are emails that exist, but for some reason, they couldn’t be delivered. Generally a soft bounce will be something temporary like an Out of Office or Mailbox Full message. Soft bounces are considered temporary until they are proven to be invalid addresses.


What should you do about soft bounces? You shouldn’t have to worry about these too much. Usually, the next time you send an email it will be resolved. You should keep an eye out for very high soft bounce rates however, as it can signal a spam blocking issue.


Soft bounces return as 400 SMTP error codes. The following chart shows the most common soft bounce categories.


Dns Failure The message bounced due to a DNS failure on the receiving ISP server. (DNS Failure)
Mailbox full The message bounced due to the remote mailbox being over quota. (Mailbox Full)
Message too large The message bounced because it was too large for the recipient. (Too Large)
Timeout The message timed out. It was not accepted by the ISP after 24 hours of attempted delivery. (Timeout)
Temporary delay Message transmission has been temporarily delayed. (Transient Failure)
No recipient No recipient could be determined for the message. (Generic Bounce: No RCPT)
Mail Block The message was blocked by the receiver. (Mail Block)
Spam Block The message was blocked by the receiver as coming from a known spam source. (Spam Block)
Spam Content The message was blocked by the receiver as spam (Spam Content)
Unknown The response text could not be identified. The receiver could not or does not want to confirm the recipient exists. (Unknown/Undetermined)
Relay denied The message was blocked by the receiver. (Relay Denied)
Prohibited attachment The message was blocked by the receiver because it contained an attachment (Prohibited Attachment)
Policy violation The message was failed by Ecelerity's configured policies. (Admin Failure)




Hard bounces

Hard bounces are always invalid addresses. The address can be invalid for two reasons: (1) the domain doesn’t exist (example: address@notrealdomain.com) or (2) the domain does exist, but the local part of the address is invalid (example: not_a_real_address@gmail.com). 


In very rare cases, the ISP may send back a hard bounce response for a valid email address. The response is still handled as a hard bounce in WordFly. You may try sending to the hard bounce again if the subscriber states the address is valid. If the address hard bounces again, the subscriber should reach out to their ISP to troubleshoot why they are sending out a hard bounce.


What should you do about hard bounces? Make sure you aren’t sending to invalid addresses. Remove bad addresses from your list immediately. Repeated sending to invalid addresses can land you on blocklists and lead to deliverability issues.


Hard bounces return as 500 SMTP error codes.


How bounces are handled

WordFly automatically handles your soft and hard bounces.


Hard bounces When this response is received by WordFly, the subscriber is flagged as an issue and removed from your future list imports. Learn about managing hard bounces.
Soft bounces When this response is received, WordFly attempts to send the email at regular intervals for up to 24 hours. We retry after 20 minutes and then wait incrementally longer after each attempt before expiring the message after 24 hours. The initial soft bounce is logged immediately. Other responses (opens, etc.) may also be logged for the subscriber if a delivery is successful.


How to view bounces

There are two ways to view soft and hard bounces for your email campaigns: Reporting > Sent Email Campaigns or Reporting > Export Data.


To view bounces under email campaign reporting

Go to Reporting > Sent Email Campaigns, select the name of your sent email, and review the Hard Bounces and Soft Bounces tabs to see bounce results. Click on the magnifying glass to see the subscribers who bounced. Soft bounces will include categories for more details (e.g., timeout, spam block, unknown, etc).



To export your bounce data by email campaign or for your entire account

Go to Reporting > Export Data and select Events by Campaign to export bounces by email campaign. Select hard bounce and soft bounce in section 3 .


Or, go to Reporting > Export Data and select Events by Account to export bounces by account. Select hard bounce and soft bounce in section 3.


Learn more about both of these export options.