plesk 11 - periodic and automatic password change for email accounts

[FastnetSpa]

I'm asking for a solution for this issue.

In Plesk 11 (linux server) i want that the password for email accounts created, could be periodically and automatically changed, and every mail account could set the new password by himself.

I've thought about using "scheduled Task" - but i need the code to insert in it - or some 3rd party application for plesk.

Could someone suggest a solution for this? The mail system associated to plesk is Horde v3.4.11.

Thanks in advance
Diego