Forwarding email and adding to Subject

==== Required information ====
- iRedMail version: 0.8.7
- Store mail accounts in which backend (LDAP):
- Linux/BSD distribution name and version: Centos 6.6
- Related log if you're reporting an issue:
====

The title says it all.

I need to be able to forward received email to a different address (while keeping a copy), and add to the subject.

I prefer to use the Roundcube managesieve plugin, but the option to modify the subject does not exist.

Thoughts?

Thanks.