← Back to Glossary

Hard bounce


What is a hard bound?

An email hard bounce occurs is when the delivery issue is permanent, such as an invalid email address.

You’ll see a hard bounce notification code that starts with a “5xx.”

Unlike a soft bounce, a hard bounce should be considered permanent.

Common reasons for a hard bounce include

A hard bounce in email delivery refers to a permanent failure to deliver an email to the recipient. Unlike soft bounces, which are often temporary issues, hard bounces indicate persistent problems. Common reasons for email hard bounces include:

  • Invalid Email Address – the recipient’s email address is incorrect, misspelled, or doesn’t exist.
  • Domain Doesn’t Exist – the domain part of the email address (after the “@” symbol) doesn’t correspond to a valid and existing domain.
  • Recipient Email Server is Down – the recipient’s email server is not operational, preventing the delivery of emails.
  • Blocked Email Address – the recipient has marked the sender as spam, or the email address is on a blacklist, resulting in blocking.
  • Email Size Exceeds Limit – the email is too large and exceeds the maximum size limit allowed by the recipient’s email server.
  • Recipient Mailbox Full – the recipient’s email inbox has reached its storage limit, and no more emails can be accepted until space is cleared.
  • Invalid Recipient Mail Server – the recipient’s email server is misconfigured or not accepting emails.
  • Syntax Errors in Email Address – the email address contains syntax errors, making it impossible to deliver the message.
  • Email Content Issues – the email content violates the policies of the recipient’s email service provider, leading to rejection.
  • Email Account Closed – the recipient’s email account has been closed or deactivated.
  • Role-Based Email Addresses – some email providers reject emails sent to role-based addresses (e.g., info@company.com) to prevent spam.

Hard bounces negatively impact email deliverability, and a high rate of hard bounces may lead to an email sender being marked as a potential source of spam. Maintaining a clean and regularly updated email list, using double opt-ins, and following best practices for email marketing can help reduce the occurrence of hard bounces.

Want to receive more great content like this for free?

Subscribe to our newsletter to get best practices, recommendations, and tips for digital marketers