Recently I had a problem while sending emails to a specific server and while looking at the logs I saw the following:
451-The server has reached its limit for processing requests from your host.
\n451 Please try again later.
T=remote_smtp defer (-53): retry time not reached for any host
The reason could either be the exim rate limiting the number of emails OR the exim databases are corrupted. In such a case, you have 2 options
1) Increase the number of emails each domain can send per hour from WHM >> Tweak Settings >> Max hourly emails.
2) If step 1 does not help, its clearly a case of exim database corruption, and to resolve the issue using the exim database tool called “exim_tidydb”. SSH to your server and execute:
# /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
Once done, reinstall courier and exim using the cPanel scripts.
# /scripts/courierup — force
# /scripts/eximup –force
You should now be able to send emails from the server.