Sometime on Cpanel servers the exim smtp report below error in the exim logs :
If exim logs show this error then the most likely reason for this problem is corruption of exim databases, specially if it reports this error for every email. To resolve this error following steps can be perform using one of exim database tools ‘exim_tidydb’ :
/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
After reinstall courier and exim using Cpanel scripts :
/scripts/courierup -- force /scripts/eximup --force
This should resolve the error.