Redmine

Hi!

I want to use redmine in our company. It is simple to use but still quite powerful.
But it lacks one important feature we really need. (It is somewhat a k.o. criteria.) And that is connected with E-Mails.
We have customers, that creates some Issues. And the customer always gets an E-Mail when we change the status. E.g. from "New" to "Implementing". But we want that they will only get an mail when we are finished with the issue. I.e. when the status changes to "Finished"

Is this somehow possible? Also, an plugin would be ok?
If not, would it be very complicated to implement an plugin that can do that? I have a little bit of Ruby/Rails knowledge but I'm not sure if this would be much to do... .

Thanks in advance for your help,
choallin