NEW BUDGET Email system like mail2web.com

I need a web mail program writing OR installing. It should be similar to [login to view URL] I need to se up accounts then users can login via a login screen on our site OR via a prepopulated url. Example: user: someperson password: access I can get into the system like this: www.thedomain.com/user=someperson&password=access It needs these features: 1. All normal email client features read / send / forward / delete etc.... 2. Sent mail needs to be kept in a separate directory. 3. Save to disk - individual messages need to be able to save to a disk. 4. Multiple email accounts on same domain - ie change from sales@ to info@ etc.... 5. Master backup - I need to be able to do one dupm to back up all sent email. You can either: 1. Write this script 2. Modify an existing script. The BEST solution will run on a server with no root access and no outgoing database connections. If this is not possible then it should run on one of our dedicated servers. The script will be checking email from several different servers - not just the one it is running on! Good luck.