2018-05-25 18:55:46.797  1fMBwM-0002Rr-MX ** firstname.lastname@example.org F=<email@example.com> R=enforce_mail_permissions: Domain abc.com has an outgoing mail suspension. Message discarded.
Received that error and to lift the suspension ran the following command through ssh:
[root@host /]# whmapi1 unsuspend_outgoing_email user=cpaneluser
Could send properly again after that.