Guide to the Secure Configuration and Administration of Microsoft ...

Select the “Delivery Restrictions” tab. These settings are advertised to restrict which
Exchange users can/cannot send outgoing messages through IMS; however, they
have no effect upon users accessing the Exchange Server through SMTP.
Exchange 5.0 Exchange 5.5
Select the “Connections” tab, check “Accept or reject by host” and select “Specify
Hosts.” Unless an Exchange server is intended for universal access, it is
recommended to restrict access.
Exchange 5.0 Exchange 5.5
Select the “Connections” tab. Unless an Exchange server is intended for universal
access, it is recommended to restrict access by use of one or more of the following:
Use the “Accept Connections” option to require authentication, encryption, or
both on all SMTP connections (applies to both client connections and
connections to other hosts).
Use the “Clients can only submit if homed on this server” option to require the
user to have a mailbox on the Exchange Server before a connection will be
allowed.
Use the “Clients can only submit if authentication accounts matches submission
address” option to help preclude a user from masquerading as another when
dropping off a message via SMTP.
Select the “Internet Mail” tab. Enable (check) “Clients support S/MIME signatures” if
S/MIME will be used.
Note: An additional IMS security related setting, “securing outbound connections”
(security tab), is discussed in Chapter 5.
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