I realize that sharing the inbox would usually be done on the mailserver itself. What I was hoping for was for a way to have Roundcube be configured so that each user has their own unique login but within the configuration of Roundcube each user really shares the same email servers account and thereby shares the same inbox. It's kind of like how when using Thunderbird, each Thunderbird client can be configured by user, but behind the scenes Thunderbird can connect to the same email account (through IMAP).