Domain x.com has exceeded the max defers and failures per hour

Reviewed on September 8, 2026 4 min read SMTP errors sending

The error "Domain x.com has exceeded the max defers and failures per hour" means the server has temporarily limited a domain's sending because of too many failed or deferred messages.

It doesn't mean you can only send ten emails an hour, even if the bounce includes something like 10/10 (83%). Those values belong to the failure protection, not to the general sending limit.

What triggers this protection

The server looks at the number of failed or deferred messages and their percentage of the account's sending. When the configured thresholds are reached, the protection may stop new messages so rejections don't keep piling up.

It can happen with a list containing old addresses, a repeated typo, a provider rejecting messages or sending you don't recognise. The error alone doesn't prove your account is being misused.

1. Find the rejection that appeared first

In cPanel, open Track Delivery and search by sender, recipient and time. Look at the details of the messages before the block, following the delivery tracking guide.

The useful information is the original reason: for example, a recipient that doesn't exist. Later rejections that only repeat "max defers and failures" show the effect of the protection.

What you find	What to do
A wrong address or domain	Correct or remove that recipient before sending again.
A temporary rejection from the receiver	Check the specific reason and avoid resending while it persists.
Many rejections from the same provider	Keep the full error text so delivery and authentication can be reviewed.
Messages you didn't send	Review the source mailbox or application with support and change the affected credentials.

Don't resend the same whole list to test: you may trigger the protection again. For mailing lists, follow the recipient list maintenance recommendations.

2. Fix the cause and check sending

Once you have corrected the recipients or the source problem, wait until the account no longer exceeds the thresholds for the hourly window. Recovery doesn't necessarily happen on the hour.

Test with one message to a valid address and check its status in Track Delivery. If it bounces again, keep the new error: there may still be an external rejection even though the local protection is no longer active.

3. When we need to review it from support

Open a ticket if you can't find earlier rejections that explain the block, if it keeps happening with normal sending or if there are messages you don't recognise. Include:

The domain and mailbox you send from.
The approximate time of a recent test.
One affected recipient and the full bounce.
Whether you send from an email app, your website or a mailing list.

With that information we can review the logs, queued messages and the protection's sensitivity. Raising the general sending limit or ordering more resources doesn't fix this problem on its own.

The cPanel documentation on mail limits explains how the failure and deferral thresholds relate.