[imp] linked attachment maintenance

[Otto Stolz]

Hello Patrick Dung,

you wrote:
> currently i know each user can config to clean up linked attachment per
> month and keep linked attchment period (6 month by default)

Whatever a user can configure for himself, the Horde administrator
can also force upon his users: just set a value, and lock it, in
imp/config/prefs.php (see horde/config/prefs.php for more details).
When the value depends on particular circumstances, you can add
the precise rules to horde/config/hooks.php.

Good luck,
   Otto Stolz