Maximum bounces per hour: causes and fix

Introduction

When a domain generates too many bounces, delivery failures or errors in a short period, the server may temporarily limit outgoing mail to protect service reputation.

This warning often appears with messages such as:

Your domain has exceeded the maximum number of bounces and errors per hour

It does not automatically mean spam, but it does show that something is causing too many failed deliveries within a short time.

What this issue means

A bounce happens when the server tries to deliver an email and receives an error response.

If too many bounces build up within an hour, the system may slow or stop sending temporarily to prevent:

• damage to domain reputation
• blocks from other mail servers
• abuse from a compromised mailbox
• repeated failures from forms, scripts or applications

Common causes

1. Misspelled email addresses

   A small typo in the recipient can create repeated delivery failures.

2. Nonexistent mailboxes

   The domain exists, but the specific address no longer does.

3. Full inboxes

   If the recipient has no available space, the message may be rejected.

4. Spam filters or receiving-server rejections

   Some servers reject messages because of reputation, internal policy or weak authentication.

5. Old or poorly maintained mailing lists

   Sending to outdated contacts greatly increases the number of failures.

6. Broken forms, stores or scripts

   An unprotected form or misconfigured application can trigger bounce chains.

7. Compromised accounts or faulty automations

   If a mailbox has been abused, it may try to send to many invalid recipients.

How to fix it

1. Review the bounced messages

Open your control panel and inspect the mail delivery tracking logs.

In cPanel this is usually Track Delivery. In DirectAdmin, the wording may vary depending on the server setup.

Look for the exact error message. For example:

550 5.1.1 User unknown

That kind of error usually means the destination address does not exist.

2. Identify the main cause

Ask yourself:

• are the addresses written correctly
• are you sending to old contacts
• are some inboxes full
• is a website or app sending without control
• does the issue affect one mailbox or several

The full bounce message matters. Not every failure points to the same root cause.

3. Correct addresses and clean your lists

Remove misspelled, nonexistent or repeatedly failing recipients.

If you use mailing lists or notifications, clean them before sending again.

4. Review forms, stores and automations

Check contact forms, WordPress, PrestaShop, CRON jobs, automatic notifications and any integration that sends mail.

Pay special attention to:

• forms without captcha
• outdated plugins
• scripts retrying failed sends
• applications sending to invalid addresses
• forwarding loops

5. Review SPF, DKIM and DMARC

If your messages are not authenticated correctly, some servers may reject them and add more failures.

Check that SPF, DKIM and DMARC exist and are configured properly.

6. Reduce bulk-sending frequency

Do not use a standard hosting mailbox for uncontrolled mass mailings.

If you need to send to many recipients, do it gradually and only with clean lists.

7. Contact support if you need a review

If the block keeps coming back or you cannot find the cause, open a support ticket and include:

• affected domain
• sending mailbox
• full error message
• approximate time of the issue
• whether the messages came from a website, campaign or application

What to do if the issue continues

If the warning appears again, do not just wait for it to clear. Fix the underlying cause.

In many cases the real source is:

• an outdated contact list
• a form sending automatic messages
• a compromised mailbox
• weak mail authentication
• a script or application repeatedly targeting invalid recipients

Useful tips

1. Keep your mailing lists clean

   Do not continue using contacts that already produced bounces.

2. Do not send to people who did not ask for it

   Unwanted mail often turns into bounces, spam complaints or blocks.

3. Protect forms and accounts

   Captcha and strong passwords reduce abuse significantly.

4. Watch for repeated errors to the same recipients

   They often reveal the easiest problem to fix.

Frequently asked questions

The warning appears even though I did not send many emails

It may come from a website, store, form, automation or compromised account.

The error only happens with some recipients

Then those addresses are probably invalid, full or being rejected by the receiving server.

Does the limit remove itself

It may be temporary, but if the cause stays active the issue will return.

Can this affect domain reputation

Yes, if it happens repeatedly. That is why the system reacts before the damage grows.

Conclusion

Exceeding the maximum bounces and errors per hour is a protection measure. It usually means something is sending to invalid recipients, full inboxes or servers that reject the message.

If you review the bounces, clean your recipients, control automations and validate SPF, DKIM and DMARC, you can usually restore normal delivery without major trouble.