The manual at http://wiki2.dovecot.org/Tools/Doveadm/Deduplicate tells how to estimate what will be expunged:
doveadm -f table fetch -u jane 'guid uid' mailbox a_Box | sort
I wanted to learn the subjects:
doveadm -f table fetch -u jane 'guid hdr.Subject' mailbox a_Box
In the output, long lines will be broken up, continuation lines starting with a blank (mostly), disabling the sort
doveadm -f table fetch -u jane 'guid hdr.Subject' mailbox a_Box \ | sed -e :a -e '$!N;s/\n\s//;ta' -e 'P;D' | sort --stable
Some (gnu) sed foo joins them back together, the sort works again :) -- peter
