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
Then goto WHM > Exim Configuration Manager > Reset Tab and select below option and click Reset.
Reset the entire Exim configuration to the default settings provided with cPanel & WHM.
After reset goto Basic Editor Tab > Domains & IP Tab and update below setting.
Send mail from the account’s IP address Off
Use the reverse DNS entry for the mail HELO/EHLO if available On
Reference /etc/mailhelo for custom outgoing SMTP HELO On
Reference /etc/mailips for custom IP on outgoing SMTP connections On
Click Save Setting.
Now goto Security Tab and save below setting.
Require clients to connect with SSL or issue the STARTTLS command before they are allowed to authenticate with the server. Off
Your outgoing email must work smoothly now.