Except for the integration with web platforms, I think you can pretty much do this with any reasonable mail client (e.g. Thunderbird) and a group IMAP account:
- Each group member configures two accounts/identities - his personal one and the group account
- Set up message forwarding from each account to the group account (e.g. if it's a Unix machine that could be the user's
.forward
file; if it's just a mail server - perhaps have each person's client run a forwarding filter on mail that's incoming to his/her personal account
- Have a single client or everyone's client have mail filtering rules on the shared account which file messages into different folders, e.g. correspondence with a member's personal address could be filed into a subfolder "personal/joesmith"
- When you reply to a message on the shared account you use the mail client UI to choose which identity you want to use
- You make sure to add copies of sent messages (both from the personal and the common account) to the shared account's mail folders, in appropriate locations
I'd say it's mostly doable. Unless you need very short reaction times, in which you can't rely on people's mail clients doing filtering when running and you'll need a more involved solution.