Hard Bounces vs. Soft Bounces: What's the Difference?

When an email can't be delivered, it "bounces." But not all bounces are created equal. Understanding the difference between a hard bounce and a soft bounce is critical for managing your email list and protecting your sender reputation.

Hard Bounces: The Red Flags

A hard bounce is a permanent delivery failure. This is a definitive signal that the email address is no good. This happens for a few key reasons:

• The email address is invalid or doesn't exist (e.g., a typo in the address or the user has deleted their account).
• The domain name doesn't exist.
• The recipient's email server has blocked delivery from your domain entirely.

Hard bounces are a serious problem. They are a strong signal to ISPs that you are sending to a low-quality list. A high hard bounce rate (anything over 2%) will quickly damage your sender reputation and can get your domain blacklisted.

How to handle them: You must remove hard-bounced email addresses from your list immediately and permanently. Most email service providers (ESPs) do this automatically after the first hard bounce, but it's essential to ensure it's happening. The best strategy is prevention: using a validation service like Cleanmails before you send is the best way to prevent hard bounces from ever occurring.

Soft Bounces: The Temporary Setbacks

A soft bounce is a temporary delivery failure. This means the email address is valid, but the email couldn't be delivered at that moment. Common reasons include:

• The recipient's inbox is full.
• The email server is down, offline, or overloaded.
• The email message is too large for the recipient's inbox.
• Your sending is being temporarily throttled by the receiving server.

Soft bounces are less damaging than hard bounces in the short term because they don't necessarily indicate a problem with the email address itself.

How to handle them: Most ESPs will automatically try to resend the email a few times over a couple of days. If an email address consistently soft bounces across multiple campaigns (e.g., 3-4 times in a row), it's a sign that the inbox is likely abandoned or no longer monitored. At that point, your ESP may start treating it as a hard bounce and remove it automatically. It's good practice to monitor addresses that consistently soft bounce and consider removing them manually to keep your list as clean as possible.

By proactively managing both hard and soft bounces, you send a clear message to ISPs that you are a responsible sender who cares about data hygiene, which is the foundation of good deliverability.