One Exchange Account and multiple users

hi all,

i have Exchange 2010 and i have some mailboxes like Info@domain.com more than one user must have access to it, i added the users to full access permissions and to send as permission, i have some problems as bewlo:

1- when the user have full access i can't add a signature to the other account.

2- so i removed the full access permission and left the send as and configured the account on the outlook as a second exchange account.

3- but now when a user receive the email and read it it shows as read for all users.

thanks

Tarek Khairy