Hello Janos,
recently I have changed the quarantine structure. Formerly it consisted by the first character of the username and the username itself, eg. .../lib/clapf/queue/j/jack
This splitting model produces balanced directories, however it requires that every user needs a unique uid. For most environments this may not be a problem, but you can have a very specific setup.
There can be a problem with virtual users. The uid is the same for all the users.
Also maybe a quarantine structure like .../lib/clapf/queue/domain/j/jack Regards, Olivier LARRIGAUDIERE