To help stop spam, the amount of emails each account sends that result in bounce backs is logged. A bounce-back email is not good, after 10 deferred / failed emails are sent in a single hour is reached, you'll have to wait one hour to send more. You should not be sending these types of email to begin with.
An email message sent that could not be delivered to one or more of its recipients will count as a deferred / failed email.
- If you are sending out mass emails and you get this error, it most likely means that:
- a subscriber is no longer using the email addresses that they subscribed with
- you are being blocked, not everyone uses the "unsubscribe" link at bottom of emails
Within cPanel there is a tool called Email Trace which can assist you in cleaning up your mailing list.
WHM / cPanel » Server Configuration » Tweak Settings
- Maximum percentage of failed or deferred messages a domain may send per hour [?]
- Unlimited default
- Number of failed or deferred messages a domain may send before protections can be triggered [?]