When you send an email, the following error can occur:
Domain example.com has exceeded the max defers and failures per hour (25/25 (100%)) allowed. Message discarded.
Reason for the error:
Your account has exceeded the allowed number of bounced messages per hour and as a result your sending rights have been blocked.
The block is temporary and is removed on the hour.
This block is required to prevent your account from being permanently blocked by third party mail servers and spam blacklist.
The block will be automatically removed on the hour. Please wait till an hour has passed to attempt to send email again.
You can also delete the file /var/cpanel/email_send_limits/max_deferfail_example.com but it is temporary fix.
To prevent max defers and failures per hour error messages please check the following:
1) Ensure your account is not sending spam. Check your mail delivery reports in your cPanel. If you see a large number of delivery failures from one of your email addresses then we recommend immediately changing your mailbox password and virus scanning all your devices.
2) Check autoresponders and spam filters. This block can sometimes be triggered when you have an autoresponder setup to send an out-of-office reply to all emails you receive. This is because the autoresponder will reply to all emails including spam email addresses which do not exist. In these cases the reply will fail which counts towards the delivery failure count per hour on your domain. To resolve this ensure your Spam Filters are enabled.
3) Check your mailing lists is up to date. If you are sending a mass marketing email, please check your mailing list is up to date by removing email addresses which no longer work. Sending to multiple invalid email addresses will trigger the block. The only way to resolve this is to clean your mail list and remove email addresses which result in bouncebacks.