really charging can be thought of as per login.....if you dont need an additional login, you dont normally pay for another user.

I wrote the below for my customers a while back, it helps them decide what type of mailbox they require.

Hosted Exchange – Recipient Types Explained

BoldStandard MailboxBold Every user requires one of these and you pay for each of these at a set fee per month, you get an email address with a username and password to sign in and connect to it. You can configure Mobiles and Tablet devices to access this type of mailbox. BoldShared MailboxBold These are free, however, to access it the user must already have their own ‘Standard Mailbox’. It is displayed as a distinct set Inbox folders separate from the user’s main account. When multiple users access the same Shared Mailbox, they can see any action performed by the other users (e.g. Marked as read, moved to folder). Users can send as a shared mailbox. A shared mailbox CANNOT be access from a mobile device such as a mobile or tablet device. BoldDistribution GroupBold These are free, when an email is received in a distribution group, a copy of this is sent to each members ‘Standard mailbox’. As each user receives an individual copy in their own inbox, users cannot see if other users have read or replied to the message. Users can send as a Distribution Group, however other members will not see the reply. BoldResource Mailbox (Room or Equipment)Bold These are free, are used to schedule access to resources such as meeting rooms, projectors and other bookable items. They are much like a Shared Mailbox, you require your own ‘Standard Mailbox’ to access it, they CANNOT be access from a mobile device such as a mobile or tablet device. Staff can create calendar bookings for access to a resource and the system can either ‘auto-accept’ requests that do not conflict with others, or pass the request to a ‘delegate’ for manual approval. BoldAlias AddressBold An alias address is a second email address attached to one of the above Recipient Types. There is no charge and emails sent to an alias address follow the same rules as the Recipient Type it is attached to. Alias emails are often used when two domains such as ‘[email protected]’ and ‘[email protected]’ are sent to the same location. This differs from other recipient types which help with different recipients at the same domain (e.g. [email protected] and [email protected]).