I am using this post to maintain a list of the useful but somewhat obscure commands for the exim MTA. Mostly for my reference but others might find it useful too.
Display all mail messages in the queue:
# exim -bp
Unfreeze all messages in the queue. This forces exim to try and send all frozen messages:
# exim -qff
Clear a single mail message from the queue:
# exim -Mrm {message-id}
Clear all mail messages from the queue:
# exim -bp | awk '/^ *[0-9]+[mhd]/{print "exim -Mrm " $3}' | bash
