The sendmail access database file can be created to accept or reject mail from selected domains.
Since "/etc/mail/access" is a database, after creating the text file, use makemap to create the database map.
# makemap hash /etc/mail/access.db < /etc/mail/access
Below is what my access file currently looks like and can be used as a starting point. All internal addresses have been changed except for spammers!!
# by default we allow relaying from localhost...
localhost.localdomain RELAY
localhost RELAY
127.0.0.1 RELAY
# Allow Connect from local server IPs
Connect:207.44.206.144 OK
# Accept Mail
# accept mail from PayPal
paypal.com OK
# Reject Mail
posterclub@e.allposters.com REJECT
posterclub@email.allposters.com REJECT
plastmarket.com REJECT
jr@jrtr.org REJECT
7b2.606@fe01.atl2.webusenet.com REJECT
mysoldpad.com REJECT
# Discard Mail
1and1-private-registration.com DISCARD
# forum admin mails:
fictionaluser@gmail.com DISCARD
# Reject full mailbox
fictionaluser@linuxweblog.com ERROR:4.2.2:450 mailbox full
fictionaluser@linuxweblog.net REJECT
# Blacklist recipients
linuxweblog.net ERROR:550 That host does not accept mail
# Spam friend domains: exempt domains from dnsbl list checking
Spam:linuxweblog.org FRIEND
# Spam friend users: exempt email users from dnsbl list checking
# example:
# Spam:user@domain.tld FRIEND
# clients
Spam:fictionalclient@hotmail.com FRIEND
# Auto REJECT via hourly cron added below