Show the mail queue
exim -bp
Process the mail queue (non force)
exim -q
Process the mail queue forcing delivery except for the frozen messages
exim -qf
Process the mail queue forcing even the frozen messages into delivery
exim -qff
Stat the mail queue
exim -bp | exiqsumm
Print out what exim is doing right now
exiwhat
Count the mail messages in the queue
exim -bpc
For further research
exiqgrep -o 86400 -i | xargs exim -MrmThe above command will delete the messages older than 1 day. To delete email more than one day you can multiply with the number of days with 86400.
Further reference: http://bradthemad.org/tech/notes/exim_cheatsheet.php