Been searching around and not really found a whole lot on what I want to do.

I need to create a few email accounts with simple generic passwords that will be shared among a few users.
These users will only be using the web interface.
I want to limit these accounts so that they may only log in from the LAN and not from the internet.
I do not want to limit all accounts, just a few.

I was thinking of having a separate mailbox server just for these accounts.
I imagine I would just have to not give it an external IP.

Would my solution work? Anyone have any simpler or better solutions?