Bounce Rate

What is Bounce Rate?

Bounce rate measures the percentage of emails that fail to deliver. It’s a key metric for list health and deliverability. Bounces are divided into two categories: hard bounces (permanent failures like invalid addresses) and soft bounces (temporary failures like a full mailbox).

Why it matters

High bounce rates signal poor List Hygiene and can severely damage your sender reputation. ISPs interpret high bounce rates as a sign of spammy behavior, which can lead to blocking or filtering. Monitoring bounce rate helps you catch problems before they spiral.

How it works

When an email fails, the receiving server sends back an SMTP error code. A "user not found" error is a hard bounce. A "mailbox full" error is a soft bounce. ESPs like AutoSend automatically add hard bounces to your Suppression List to prevent further harm.

Examples

• Sending to a purchased list full of invalid emails (hard bounces).

• A holiday campaign landing in full inboxes (soft bounces).

• Old corporate addresses bouncing after employees leave.

Best practices

• Validate emails at collection to prevent typos.

• Regularly clean your lists to remove inactive or invalid addresses.

• Monitor bounce reports to detect systemic issues.

Related terms

Bounced Emails, Invalid Emails, Suppression List

FAQs

What’s an acceptable bounce rate?
Under 2% is generally considered healthy. Anything higher signals problems with acquisition sources, data quality, or technical setup. Persistent high bounce rates can lead to blacklisting.

What’s the difference between hard and soft bounces?
Hard bounces are permanent (invalid domain, user doesn’t exist). Soft bounces are temporary (mailbox full, server unavailable). ESPs typically retry soft bounces for a period before treating them as failures.

How do I reduce bounce rate?
Focus on prevention: validate addresses at signup, use double opt-in, and avoid buying lists. Also, monitor engagement and suppress addresses that haven’t interacted with your emails for months.