After receiving this call it occurred to me that not many people consider posting basics out there and with this being a heavily used feature in many situations, so I thought I’d explain the steps for anybody in need of some advice in this sort of thing. I’ll drop a few pictures in as we go along after the descriptions, just to see the sort of screen we should be looking at.
The first thing that we want to do is obviously log onto our exchange server and make sure that we’re on the Recipients Section (located on the left hand side) and also in the Mailboxes Tab (located at the top of the page).
You then want to go ahead and add the Mailbox that you’ll be granting the send as permissions for by click the + (Top of the page). Then you want to select the User Mailbox Option.
A window will then be displayed showing a new user mailbox and you’ll want to select the New User radio button and make sure that you’ll fill in the required fields.
Towards the bottom of this form there will also be a Password section but due to this being a shared mailbox… you will be granting Full Access and Send As permissions so they should not need the password. An important note on the other hand is to use a password that will be remembered for any future cases that may require the password.
You will also want to make sure that the OU you choose is users as I have recently encountered a problem of choosing the wrong OU.
You will also see the More Options link at the bottom of this form and in this separate window that opens you will also want to choose the appropriate mailbox database.
The next step is to add our appropriate users into the Shared Mailbox so you will want to select the mailbox (shown as Example below) and you’ll need to click the edit icon 
(next to the add icon)
You will then see a window displayed with the general tab open, on the left hand side select the ‘Mailbox Delegation’ tab to be presented with the Send As and Full Access screen. Full Access will be located further down the form and will be seen if you use the scroll bar located on the right hand side.
If you then click the Add Icon 
it will display another window with the users you can select. If you cannot see the user you need on the initial screen, type the name into the search bar to find them and then upon clicking on their name, followed by add-> at the bottom (or double clicking) they will be added to the this particular Mailbox Delegation.
After finding all of the users you need for Send As, Send on Behalf and Full Access make sure that you click the Save button to make sure your changes have been made.
Following on from this process in can sometimes take some time for this to update in the offline address book.
Thanks for reading and I hope this helps!
J
