How to Manually Grant Send As Permissions to a User with Full Mailbox Access
To manually grant Send As permissions to a user with full mailbox access (as shown in the figure), perform the following procedure.
With full mailbox access, User A logs on to User B's mailbox and sends mail while acting as User B
Before You Begin
Be aware that previous versions and service packs of Exchange Server 2003 have varied in how they implement Send As and Receive As permissions. For more information about when this behavior changed, see the release notes for Microsoft Exchange 2000 Server and its service packs (available in the Microsoft Knowledge Base).
To manually grant Send As permissions to a user with full mailbox access
In Active Directory Users and Computers, right-click the organization domain name, point to View, and then click Advanced Features.
Click the Users container or the organizational unit where the user is located.
Right-click the user account, and then click Properties.
Click Security, and then click the user or group to whom you want to grant permissions. You may have to add the user or group to the list.
Click Send As, and then select the Allow or Deny check boxes as appropriate.