To re-edit retry configuration in exim.
# vi /etc/exim.conf
Then search for RETRY CONFIGURATION in configuration file and do the needed changes.
# Domain Error Retries
* * F,2h,15m; G,16h,1h,1.5; F,4d,8h
This single retry rule applies to all domains and all errors. It specifies retries every 15 minutes for 2 hours, then increasing retry intervals, starting at 1 hour and increasing each time by a factor of 1.5, up to 16 hours, then retries every 8 hours until 4 days have passed since the first failed delivery.