Apple Mac OS X Server (Administrator’s Guide) - Manual (Page 398)

398 Chapter 9
Limiting Junk Mail
You can configure mail settings to decrease the amount of junk mail that your mail service
delivers to users. You can also take steps to prevent senders of junk mail (spam) from using
your server as an open relay. If you allow junk mail senders to use your server as a relay
point, your server may be blacklisted as an open relay, and other servers may reject mail from
your users. Your mail service can do the following to reduce spam:
m Require SMTP authentication so that your server cannot be used as a relay point by
anonymous users. For instructions, see “Requiring SMTP Authentication” on page 389.
m Restrict SMTP relay, allowing relay only by approved servers on a list that you create. For
instructions, see “Restricting SMTP Relay” on page 398.
m Reject SMTP connections from specific servers on another list that you create. For
instructions, see “Rejecting SMTP Connections From Specific Servers” on page 399.
m Log and optionally reject an SMTP connection from a server whose DNS name doesn’t
match a reverse-lookup of its IP address. For instructions, see “Checking for Mismatched
SMTP Server Name and IP Address” on page 399.
m Reject SMTP connections from servers that are blacklisted as open relays by an Open
Relay Behavior-modification System (ORBS) server. For instructions, see “Rejecting Mail
From Blacklisted Senders” on page 401.
m Allow or deny SMTP connections from specific IP addresses by using the firewall service
of Mac OS X Server. For instructions, see “Filtering SMTP Connections” on page 401.
Restricting SMTP Relay
Your mail service can restrict SMTP relay by allowing only approved servers to relay mail. You
create the list of approved servers. Approved servers can relay through your mail service
without authenticating. Servers not on the list cannot relay mail through your mail service
unless they authenticate first. All servers, approved or not, can deliver mail to your local mail
users without authenticating.
Your mail service can log connection attempts made by servers not on your approved list.
To restrict SMTP relay:
1 In Server Settings, click the Internet tab.
2 Click Mail Service and choose Configure Host Settings.
3 Click the Incoming Mail tab.
4 Select “only hosts in this list” and then edit the list of servers.
Click Add to add a server to the list.
Click Remove to delete the currently selected server from the list.
When adding to the list, you can use a variety of notations.