For creating a shared mailbox in office 365, you have to first create a normal mailbox. If you are in a staged environment or even hybrid deployment, you first create a normal mailbox in on-premise exchange and sync it to the cloud.

Now you should have a mailbox in office 365. Once you have that, you can convert that mailbox type to Shared, so that it becomes a shared mailbox without a licence. The advantage is that if you use a normal mailbox, you need to assign a licence. If you convert it to 'Shared Mailbox', you do not need to assign licence. But you can give other licenced users, access rights to this shared mailbox which will have 5GB of storage space and also you can decide on who needs to have 'Send As' permissions.

In this example, the company is in a staged migration, with single sign on and directory sync. So the email '[email protected]' is under 'generic accounts; in the on-premise AD. After sync, the same email is synced to the office 365. There is another user named [email protected]. Here, the [email protected] email is converted to 'Shared Mailbox' and [email protected] is given permission to access the inbox and 'SendAs' [email protected]. The following steps will achieve this.

1. First create the SendAs rights for the shared mailbox

First install powershell and follow the procedures as provided in this url before proceeding further. <a href="http://help.outlook.com/en-us/140/cc952755.aspx">http://help.outlook.com/en-us/140/cc952755.aspx</a>&#160;

Once you have completed all the steps in the above url, continue below.

Open the powershell and type in the following command

  Add-RecipientPermission -Identity [email protected] -Trustee [email protected] -AccessRights SendAs 

  PS C:\Windows\system32> Add-RecipientPermission -Identity [email protected] -Trustee [email protected] -AccessRights SendAs 

  Confirm

  Are you sure you want to perform this action? 
    Adding recipient permission 'SendAs' for user or group 

    '[email protected]' on recipient '[email protected]'. 

    [Y] Yes  [A] Yes to All  [N] No  [L] No to All  [?] Help (default is "Y"): Y 

  Identity        Trustee         AccessControlTy AccessRights    Inherited 
                                    pe 

    --------        -------         --------------- ------------    --------- 

    Adam One        Ashley----..... Allow           {SendAs}        False

2. Check if the SendAs permissions are granted properly. 

Get-RecipientPermission -Identity [email protected] | Select Trustee, AccessControlType, AccessRights </>

  PS C:\Windows\system32> Get-RecipientPermission -Identity [email protected] | Select Trustee, AccessControlType, AccessRights 

  Trustee                    AccessControlType          AccessRights 
    -------                    -----------------          ------------ 

    NT AUTHORITY\SELF          Allow                      {SendAs} 

    Ashley J... Allow                      {SendAs}

3. Now Grant 'FullAccess' rights for the shared mailbox 

  Add-MailboxPermission -Identity [email protected] -User [email protected] -AccessRights FullAccess -InheritanceType All 

  PS C:\Windows\system32> Add-MailboxPermission -Identity [email protected] -User [email protected] -AccessRights FullAccess -InheritanceType All 

  Identity             User                 AccessRights        IsInherited Deny 
    --------             ----                 ------------        ----------- ---- 

    Adam One             APCPRD03\ashley52... {FullAccess}        False       False

4. Verify that the permissions are applied to Mailbox ID 1, use the following command: 

  Get-MailboxPermission -Identity [email protected] | Select User, AccessRights, Deny

In the results, you should be able to confirm that <Mailbox ID 2> has Full Access rights granted.

5. Now, convert the mailbox type to Shared. 

   PS C:\Windows\system32> set-mailbox [email protected] -type Shared 
    PS C:\Windows\system32>