Partition queue directories into hashed subdirectories
Original LP Author: Sumana Harihareswara , LP Link: https://bugs.launchpad.net/bugs/1414178
Partition queue directories into hashed subdirectories so that all queue files do not live in the same directory (which increases contention on the directory inodes and reduces overall performance).
From http://wiki.mailman.psf.io/DEV/Mailman%203.0?action=diff&rev2=30&rev1=28 -- a TODO for the Mailman 3.x series.