HP-UX Mailing Services Administrator's Guide

Configuring and Administering Sendmail
Modifying the Default Sendmail Configuration File
Chapter 256
You must enable this option only if absolutely necessary because it opens
a window for spammers. Specifically, spammers can send mail to your
mail server that claims to be from your domain (either directly or
through a routed address), and you can then go ahead and relay it out to
arbitrary hosts on the Internet.
Blacklist recipients This feature enables Sendmail to block incoming
mail messages destined to certain recipient user names, host names, or
addresses. This feature also restricts you from sending mail messages to
addresses with an error message or REJECT value in the access
database file. For example, if you have the following entries in the access
database file:
badlocaluser 550 Mailbox disabled for this username
host.mydomain.com 550 That host does not accept mail
[e-mail] 550 Mailbox disabled for this
recipient
These entries prevent a recipient of [e-mail], any
user at host.mydomain.com, and the single address
[e-mail] from receiving mail.
[e-mail] REJECT
cyberspammer.com REJECT
The entries in the access db file indicate that Sendmail cannot send mail
messages to [e-mail] or to the domain cyberspammer.com.
Accept unresolvable domains Setting this option, allows Sendmail
to accept all those MAIL FROM: parameters that are not fully qualified,
that is, if the host portion of the argument to MAIL FROM: command
cannot be located in the host name service (for example, DNS).
Accept unqualified senders This option allows Sendmail to accept
all those MAIL FROM: parameters where the mail address of the sender
does not include a domain name. Normally, MAIL FROM: commands in
the SMTP session are refused if the connection is a network and the
sender address does not include a domain name.
Realtime Blackhole List Setting this option, turns ON the rejection of
hosts found in the Realtime Blackhole List. The default list is
maintained on the server $def_rbl. This option has now been
deprecated.