This is a tip for the pepole works with web hosting.
CPANEL has the exim as the default MTA, and this tip is usefull on server administration.
Well, if your mail spool of exim is full and you need to clean this ... here is the command to do this.
exim -bp | awk '/^ *[0-9]+[mhd]/{print "exim -Mrm " $3}' | bash
Another interesting command is :
exim -bp | exiqgrep -i | xargs exim -Mrm
The original post ( in portuguese) is here.