On the Start menu, point to
Programs, point to Administrative Tools, and then
click Active Directory Users and Computers.
In the console tree, expand the Windows 2000 domain.
Double-click Users, or double-click the node that contains
the recipient information you want to modify.
In the details pane, double-click the mail-enabled recipient
you are modifying.
On the Exchange General tab, click Modify.
In the E-mail Address dialog box, select Modify
existing e-mail address, and then click OK.
On the General tab, in E-mail address, change the
e-mail address, and then click Apply.