Bounced Email Defined

A bounced email is an email that is rejected by the server and is not delivered to its intended destination. 

There are many reasons why an email may “bounce.” For example, an email may bounce if the email address doesn’t exist, if a recipient’s inbox is full, or if a server outage occurs. Poor sender reputation due to spam complaints or flagged content can also contribute to bounce rate. Understanding what caused an email to bounce can help you adjust your email strategy to improve deliverability and engagement.

For a detailed look into optimizing emails for deliverability, leverage the OneSignal Email Performance Guide for best practices.

How to Use it in a Sentence

Regularly removing unengaged emails from your send lists can help reduce your number of bounced emails.

Common FAQs

When an email bounces, you will receive an automatic response providing the general reason for the bounce. This message typically includes:

  • The time and date that the bounce occurred
  • Your Email Service Provider (ESP) IP and name
  • An error message

Looking at this auto-response can help you determine if it was a hard bounce or a soft bounce.

A soft bounce means that there’s a temporary issue that’s causing an email to bounce. A hard bounce means that there is a permanent reason why an email cannot be delivered. Typically, ESPs will consider a failed delivery attempt as a hard bounce after three soft bounces.

Some common reasons for a soft bounce include:

  • The email is “undeliverable”— An undeliverable email can be the result of a temporary server outage or the server undergoing maintenance. If this issue persists, the server could be permanently gone.
  • The recipient’s inbox is full— A soft bounce can also be a symptom that your recipient’s mailbox is too cluttered and can’t accept any more messages. This can also mean that your contact has stopped using this email address, so you may want to follow up with them via another channel to update their information in your system.
  • The email fails to meet server requirements— Your message doesn’t meet the recipient server’s anti-spam, anti-virus, or DMARC authentication requirements.
  • There's an issue with message size—Your email message is too big.
  • You receive an autoreply — If your contact is gone on vacation or is otherwise out of the office, your emails to them will bounce.

Some common reasons for a hard bounce include:

  • The email address doesn’t exist — This can happen due to a recipient misspelling their email, or leaving the affiliated organization.
  • The email address is fake — this may happen if you offer something in exchange for a contact email.
  • The email is blocked — This occurs when the receiving email server has rejected your email. Either your recipient intentionally blocked you, or their domain has stringent spam filter settings.

Your email bounce rate can be defined as the percentage of your emails that bounced. To determine your bounce rate, take the number of bounced emails and divide by the total number of emails sent and multiply by 100.

Bounced Emails/ Total Emails Sent x 100 = Bounce Rate (%)

A good bounce rate is generally equal to or lower than three percent of your total emails sent.

There are a variety of ways to reduce your number of bounced emails and protect your sender reputation. Check out our article on the five most effective strategies to reduce your bounce rate.