I found a way to find and delete from exim queue messages sent using an authenticated account (useful to purge queue from spam sent by a compromised account):
find /var/spool/exim/msglog -exec grep -l login:email@example.com {} \; | sed 's/\/var\/spool\/exim\/msglog\/.\///' | xargs exim -Mrm
Now I would like to write a shell script delq.sh so I can run ./delq.sh mail@example.com
to do it, but tried various combinations of quotes but was not able to make find ... -exec login:$1 ...
working.