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Why am I seeing email bounces and tips for improving email deliverability

Learn why emails may not be delivered to the recipients and how to reduce bounces

In this article, you’ll learn what an email bounce is, types of bounces, common reasons why emails bounce, and how to improve deliverability and reduce your chances of emails bouncing.

What is an email bounce?

An email bounce, commonly referred to as bounced email or bounce-back, occurs when an email message cannot be delivered to the intended recipient and is returned to the sender's email server. 

What causes an email to bounce back?

Several factors can contribute to an email bouncing back to the sender. Here are some common reasons:

  • Invalid or mistyped email address: Around 20% of all email bounces occur due to incorrect recipient email addresses. (Source: HubSpot)
  • Full mailbox or exceeded storage limits: Approximately 30% of email bounces are caused by recipient mailboxes being full or exceeding storage limits. (Source: Campaign Monitor)
  • Spam filters blocking the email: Spam filters account for 10-20% of email bounces, often flagging legitimate emails as spam. (Source: Litmus)
  • Domain-related issues: Domain-related issues, such as misconfigurations or expiration, contribute to about 10% of email bounces. (Source: SendGrid)
  • Temporary server issues or downtime: Server-related issues cause around 15% of email bounces, resulting in temporary delivery failures. (Source: Constant Contact)
  • Message size exceeding recipient server limits: Approximately 5% of email bounces occur due to messages exceeding recipient server limits. (Source: Mailgun)
  • Recipient's email server misconfigurations: Misconfigurations on the recipient's email server contribute to 10-15% of email bounces. (Source: Mailchimp)

Types of email bounces

Email bounces can be categorised into two main types: 

  • Soft Bounces: Soft bounces are temporary delivery failures that occur due to issues like a full mailbox or temporary server problems. The email may be retried for delivery over a certain period before being considered a hard bounce.
  • Hard Bounces: Hard bounces are permanent delivery failures caused by issues like invalid email addresses or permanent server errors. These emails are typically not retried for delivery.

Identifying the type of bounce helps in determining the appropriate course of action to resolve the issue and prevent future occurrences.

How to prevent email from bouncing back and improve email deliverability

Here are some strategies to minimise bounce-backs:

  • Verify recipient email addresses: Ensure email addresses are accurate and up-to-date before sending emails. Within Firmable, you can also filter on email deliverability measures to limit your sends to those with a strong likelihood of accuracy for optimal delivery rates. Learn more on how to use email deliverability filters in Firmable.

  • Comply with the relevant spam regulations for the country you’re sending emails to. Learn more about the Spam Act from ACMA for Australia, and follow best practices for email marketing and communication to avoid triggering spam filters. This includes:
      • Getting consent: Ensure you have either express or inferred consent from recipients before adding them to your email list.
      • Clearly identify yourself as the sender: Accurately identify your name or business name, and include correct contact details too.
      •  Providing opt-out options and making it easy to unsubscribe: Include clear and easy-to-find opt-out options in your emails, allowing recipients to unsubscribe from future communications.
  • Avoid typos within your email content: Double-check email content including subject lines and message text to minimise the risk of typos that could lead to being identified as spam and bouncing.

  • Monitor mailbox status: Check the status of recipient mailboxes to prevent issues related to full mailboxes or exceeded storage limits. 

  • Use clear subject lines: Avoid deceptive or misleading subject lines that may be flagged as spam and clearly communicate the purpose of the email.

  • Avoid spammy content: Refrain from using spam-like content, such as excessive use of capital letters, multiple exclamation marks, and misleading claims.

  • Authenticate your emails: Implement email authentication protocols like SPF (Sender Policy Framework), DKIM (DomainKeys Identified Mail), and DMARC (Domain-based Message Authentication, Reporting, and Conformance) to verify the legitimacy of your emails and increase deliverability rates.

  • Maintain DNS (Domain Name System) and domain integrity: Regularly monitor and address any DNS or domain-related issues to ensure smooth email delivery.

  • Stay informed about server status: Keep track of email server status and promptly address any downtime or maintenance issues.

  • Optimise message size: Avoid sending emails with excessively large attachments or content that may exceed recipient server limits.

  • Collaborate with IT departments: Work closely with IT departments or email administrators to address any server or configuration-related issues.

Email bouncing may still happen regardless of whether the email address is correct, however you can take proactive steps to minimise the impact. By implementing the strategies outlined in this article you can significantly reduce email bounce rates.

What happens if I get email bounces from Firmable data?

We suggest reviewing this article and the practices within it that help to reduce bounce rates. For any hard bounces that indicate an invalid email address, we would love to know about it! Please contact support@firmable.com or your account manager. For any bounce reports with invalid emails provided, we’ll happily credit you for the bounces and use this information to continue to improve the Firmable database.


Learn more about how Firmable ensures email verification for better deliverability.