About bounces (hard/soft)

A bounce occurs when an email you send cannot be delivered and is returned to Flexmail's servers. Bounces are a normal part of email sending, but keeping your bounce rate in check is important for your deliverability and your sender reputation.

Your bounce data is available in every campaign report under the Deliveries section.

Hard bounces

A hard bounce means the email could not be delivered and is unlikely to succeed in future attempts. Hard bounce codes start with 5. Common causes:

• The email address no longer exists
• The domain no longer exists
• The receiving server permanently rejected the message

What Flexmail does with hard bounces

For the specific code 5.1.1 (email address does not exist), Flexmail immediately moves the address to your blacklist with the reason "hard bounce." This is the most reliable indicator that an address is invalid.

For all other hard bounce codes (starting with 5), Flexmail counts consecutive bounces. By default, after 3 consecutive hard bounces across separate campaigns, the address is moved to your blacklist. This threshold can be configured in Settings, then Configure bounces.

Soft bounces

A soft bounce is usually temporary. The email could not be delivered right now but may succeed in a future attempt. Soft bounce codes start with 4. Common causes:

• The recipient's mailbox is full
• The receiving mail server is temporarily unreachable
• The message was too large
• The server was temporarily rate limiting incoming email

What Flexmail does with soft bounces

Soft bounces are retried automatically. A contact with a soft bounce is not immediately blacklisted. However, if an address continues to soft bounce across multiple campaigns, Flexmail eventually treats it as a hard bounce and removes it from your active list.

Bounce codes explained

Bounce codes are standardised three-digit numbers. The first digit tells you the category:

• 4xx: temporary failure (soft bounce)
• 5xx: permanent failure (hard bounce)

The full code gives more detail. For example, 5.1.1 means the email address does not exist; 4.2.2 means the mailbox is full. Your campaign report shows the bounce code for each bounced address so you can understand what went wrong

Why your bounce rate matters

A high bounce rate signals to internet service providers that you are not maintaining your list properly. Too many hard bounces can lead to your emails being filtered or blocked, not just for the specific campaign but for all your future sends.

As a guideline, keep your bounce rate below 10%. If you are consistently above this, review your contact acquisition practices and consider a list hygiene exercise to remove addresses that have never engaged.

Common mistakes to avoid

Ignoring bounce data in campaign reports

Bounce rates are easy to overlook when you are focused on open rates and clicks. But a growing bounce rate is an early warning sign of list quality problems. Check the Deliveries section of your campaign reports regularly.

Not configuring the bounce threshold

The default threshold is 3 consecutive hard bounces before an address is blacklisted. For most accounts this is fine, but if you send infrequently, a contact could accumulate bounces over a long period before being removed. Review your bounce settings in Settings, then Configure bounces.

Trying to keep bounced addresses on the list

Some users try to remove hard-bounced addresses from the blacklist and re-import them in hopes that delivery will work this time. It rarely does, and repeated sending to invalid addresses accelerates sender reputation damage.

Next steps

• Read "Configure bounces" in Settings to adjust the hard bounce threshold for your account
• Read "Manage blacklisted contacts" to understand what happens once a bounced address reaches the blacklist
• Read "Campaign reports" to see where bounce data appears for individual campaigns

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