1. Start Active Directory Users and Computers; click Start, point to Programs, point to Administrative Tools, and then click Active Directory Users and Computers.
2. On the View menu, make sure that Advanced Features is selected.
3. Double-click the user that you want to grant send as rights for, and then click the Security tab.
4. Click Add, click the user that you want to give send as rights to, and then check send as under allow in the Permissions area.
4.5 Remove all other permissions granted by default so only the send as permission is granted.
5. Click OK to close the dialog box.