Installing and Administering Internet Services

Chapter 4 197
Installing and Administering sendmail
Configuring sendmail to Reject Unsolicited Mail
Screening Incoming Network Connection Requests
The check_relay ruleset allows you to examine incoming network
connections and accept or reject them based on hostnames, domain, or IP
addresses.
To reject relay access to specific hosts, specify the IP address of the host
in the /etc/Mail/DeniedIP file.
15.10.43.248
15.10.43.245
You can also specify the name of the host you want to deny access in the
file /etc/Mail/DeniedNames. You must enter the Fully Qualified
Domain name, for example, bobcat.rose.hp.com.
Sendmail Validation
The check_compat ruleset compares all senders and receiver pairs
before mail is delivered. It validates the mail based on the results of the
comparison. It checks to see if host A can legally send a message to host
B. check_compat is called for all mail deliveries, not just SMTP
transactions.
It is used in the following situations:
• A set of users who are restricted from sending mail messages to
external domains need to send mail messages to internal; domains.
Both the sender and recipient addresses are checked to ensure that
they are in the local domain.
• A particular user needs to ensure that he or she does not receive mail
messages from a specific source.
• A particular host needs to ensure that external senders do not use
that host as a a mail relay. The mail messages are screened based on
the sender’s hostname.
Sendmail Anti-Spamming Security
The anti-spamming features enable you to control which users can send,
receive, or relay mail messages on the network. Sendmail provides the
following features:
• Using the Access Database to allow or reject mail from specific
domains