If using cPanel with CentOS, as root user run the following:
cd /var/spool/exim/db
rm -f retry retry.lockfile
rm -f wait-remote_smtp wait-remote_smtp.lockfile
service exim restart
Or, use the following commands:
/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
