Sharing or not sharing the INBOX

Hi,

I am using Dovecot and Sendmail ( as lmtp server )

I  would like to consider having some users using there emails and having their "private Ibox" ( I would say as a normal use )

and some users sharing their Inbox

1. Should I consider using and configure 2 different email servers ? ( one sharing the inbox of any users, the other one, not sharing the inbox...)  or I can have this config with the same email server ?

2. if so, how to tell Dovecot to get for user1 and user2 the same Inbox and (user3 and user4) Not sharing their inbox ?  - ... like private emails and a tech support, which should share the same folder

3. or Can I say : User1 -> User 4 have private emails Inbox.. but user3 and user4 are also sharing the same folder /var/spool/mail/support/  for example

I should admit that I don't know where to go :-(

Thanks for your help