Smart hosts clients can send but cannot receive

Hi i am running the following version of cpanel, i had smart host working fine until a few days ago that clients reported that they cannot receive emails but they can only send. /etc/redhat-release:CentOS release 6.10 (Final) /usr/local/cpanel/version:11.82.0.9 /var/cpanel/envtype:vmware CPANEL=release