Remove option to attach anything to a single email user

==== Required information ====
- iRedMail version: 0.8.7
- Store mail accounts in which backend (LDAP/MySQL/PGSQL): LDAP
- Linux/BSD distribution name and version: Ubuntu 12.04.3 LTS 64-bit
- Related log if you're reporting an issue:
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Hi, is it possible to remove the option to attach or restrict one user to attach anything to his/her emails?

Thanks!