T=remote_smtp defer (-53): retry time not reached for any host

This can be caused by multiple things, however if it happens for each email, it’s likely your exim databases are corrupt; to resolve this you should:

/usr/sbin/exim_tidydb -t 1d /var/spool/exim retry > /dev/null
/usr/sbin/exim_tidydb -t 1d /var/spool/exim reject > /dev/null
/usr/sbin/exim_tidydb -t 1d /var/spool/exim wait-remote_smtp > /dev/null

/scripts/courierup — force
/scripts/eximup –force

If you did that, yet the problem persists, you can either seek professional help, or contact the cPanel support.