Technical data

Configuring and Managing SMTP
17.6 Configuring SMTP AntiSPAM
against the Good-Clients list occurs, the client is considered ‘‘unknown’’ and
the process goes to step 2.
2. When the client is unknown, the domain of the address in each RCPT TO
command is checked against the Relay-Zones list. If a match occurs, the
RCPT TO command is accepted, because it is a relay from the unknown world
to the known world (for example, e-mail from the Internet). If a match does
not occur, the RCPT TO is considered unacceptable for route-through.
17.6.3 Controlling Relay Checking
If neither Good-Clients nor Relay-Zones is configured, relay checking depends on
the setting of the SMTP configuration relay flag. If the relay flag is set, all relays
are allowed; if it is not set, relays are not allowed.
To use Good-Clients and Relay-Zones lists, you must still set the SMTP
configuration relay flag. Use the following command:
TCPIP> SMTP SET CONFIGURATION/OPTION=RELAY
Although the configuration of both Good-Clients and Relay-Zones at the same
time makes sense for most configurations, it is not required that both be
configured. If a Relay-Zones list is specified without a Good-Clients list, relay
checking depends on the setting of the relay flag. Information in the Relay-Zones
list is ignored.
If you specify a Good-Clients list but no Relay-Zones list, the host will relay
mail from SMTP clients matching the Good-Clients list but will not relay any
mail from unknown SMTP client hosts. The host will accept mail only from an
unknown SMTP client host if it is local mail (mail destined to the local host
or a host listed in the local aliases list). If you want the host to accept relay
mail from unknown SMTP client hosts, you must specify Relay-Zones or enable
Relay-Based-On-Mx (described in Section 17.6.3.3).
17.6.3.1 Specifying the Good-Clients List
The Good-Clients list is a comma-separated list of clients, specified as one of the
following:
• IP address
• IP network
• DNS hostname
• DNS MX domain
To enter an IP network, use the n.n.n.n/m syntax, where n.n.n.n is the IP
network and m is the number of bits in the subnet mask. For example:
Good-Clients: 1.2.0.0/16, 2.3.0.0/16,
2.3.4.5, relay.abc.com
This Good-Clients list contains two IP networks (1.2.0.0 and 2.3.0.0), an IP
address (2.3.4.5), and a DNS entry ( relay.abc.com ). An entry that does not
follow the standard IP address or network format is assumed to be a DNS entry.
Configuring and Managing SMTP 17–19