Assume the following - this assumes that the Exchange Management Console is being used to modify permissions:
You have a mailbox with an email address of "UserA@example.com"; User B asks if they can be given access to this mailbox. Access is granted
User C then requests access to the "UserA" mailbox, as well as User B; despite previously adding User B's permissions, this is done at the same time as User C
In the above example, is an error thrown when choosing to give Full Access Permission from within the EAC? I know that for Active Directory security groups, if using the ADUC snap-in, an error is displayed stating that a user already has access to a group if you attempt to add duplicate permissions but I wasn't sure if this was also true for Exchange.