Error: Domain has exceeded the max defers and failures per hour (5/5 (100%)) allowed

One of our client was getting email failure messages from a domain name  hosted on our server, The error was like:
[wpfmb type=’error’ theme=2]“Domain has exceeded the max defers and failures per hour (5/5 (100%)) allowed” .[/wpfmb]
This error occurs when an account sends email to addresses that fail or defer more than the set limit and Exim restricts them from sending any email out of your server.  If the define limit within the WHM is 50% or lower, Mail will be rejected when that account sends more emailS and if any 5 email failures.
We can change the threshold or disable this feature within the cPanel/WHM
Deferred messages

  1. Log into the WHM as root
  2. Click tweak settings
  3. Click the Mail tab
  4. Scroll down and find the “Maximum percentage of failed or deferred messages a domain may send per hour” setting
  5. Change the % or you can disable this feature by selecting the Unlimited option.