Is it possible to add a field to the messages using a API based Plugin???

[infoal]

Hi everybody, i've just discovered roundcube, and i'd like to start developing a plugin, but i dont know if the API is powefull enough to do what i want.
I've experience developing joomla and prestashop plugins in php.

My idea is to add the "priority" field to the messages. 
A little dropdown list can be added in the right corner of the messages, and the user can select a priority value from 0 to 9.
Then, the message list will be ordered by priority, the most important messages will be on top.
By this way, roundcube can be used as a task manager.

I know that it's not really dificult to do this hacking some core files and adding the priority filed to the database, but, can somebody confirm if it's possible to do this using an API Plugin?
Thanks a lot!

[SKaero]

The hard part will be doing the actual sort but I think you should be able to work it out. Take a look at the plugin hooks http://trac.roundcube.net/wiki/Plugin_Hooks and see if there is anything your missing.