-This feature can be implemented as a policy
-The reason is a problem with old archive mail databases ACL overwriting.
Most organisations keep archives of deleted users. (e.g. T: a_apolak.nsf) and mail server is trying to create new archive file for a new different user e.g. Anna Polak in the same location, also as a_apolak.nsf archive - >which gives Anna access to Adam's unencrypted mail.
-If there is a way to customise the shortname, for eg: adding a current date suffix to the mailfile name(which comes from shortname) then such situations can be avoided.