How to solve Mail bounce back – retry time not reached for any host after a long failure period

When domain email accounts getting bounce back message with the error: T=remote_smtp: retry time not reached for any host after a long failure period 1.) Go to /var/spool/exim/db 2.) delete files: retry , retry.lockfile , wait-remote_smtp, wait-remote_smtp.lockfile 3.) service exim restart