2016-01-07 14:46:27 [638255] 1aB91I-002g1R-Gw ** to@address.com <to@address.com> F=<user@example.com> R=enforce_mail_permissions: Domain example.com has exceeded the max defers and failures per hour (5/5 (100%)) allowed. Message discarded.
Tweak Settings >> Number of failed or deferred messages a domain may send before protections can be triggered
Also in WHM >> Modify an Account there is the setting there: “Maximum percentage of failed or deferred messages a domain may send per hour.” “Maximum Hourly Email by Domain Relayed”
to reset the limit:
vim /var/cpanel/email_send_limits/max_deferfail_example.com
or just remove it:
rm /var/cpanel/email_send_limits/max_deferfail_example.com