Exim
show mail queue
mailq exim -bp
flush mail queue
runq exim -q
force delivery attempt
exim -qf (non-frozen messages) exim -qff (all messages, frozen or not)
deliver just one specific mail from queue
exim -M [queue-id]
(the queue-id is what you see after the size and before the email address)
search for specific mails in the queue
exiqgrep -f <sender address> exiqgrep -r <recipient address> man eqixgrep for more options