For mailbox-enabled users, you can select an option that
automatically downgrades e-mail that is set for high priority
delivery to an X.400-type e-mail address. This downgrade causes the
outbound e-mail to conform to original 1984 X.400 conventions.
On the Start menu, point to
Programs, point to Administrative Tools, and then
click Active Directory Users and Computers.
In Active Directory Users and Computers, on the
View menu, click Advanced Features.
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 mailbox-enabled user you
are modifying.
On the Exchange Advanced tab, select the Downgrade
high priority mail bound for X.400 check box.