Mail Queue Retry Limit
The retry period is controlled by Sendmail.
To change it, edit /etc/mail/sendmail.mc on your CanIt server. You should see a line that looks like this:
That makes Sendmail give up trying to deliver a delivery-status notification after 12 hours. The default for all other mail is five days. If you want to change it (for example, to seven days) add the following line below the previous line:
make -C /etc/mail && /etc/init.d/sendmail reload
to cause the new setting to take effect. A time period in Sendmail is specified by a number followed by a letter: s = seconds, m = minutes, h = hours and d = days.