I am trying to fine tune the main.cf and I am trying cut down the
number of spam thats
coming through.

In this company so far they have in main.cf file:

smtpd_recipient_restrictions =
permit_mynetworks,
reject_unauth_destination
check_recipient_access dbm:$config_directory/recipient_access,
check_client_access dbm:$config_directory/access,
check_client_access dbm:$config_directory/helo_access,
reject_non_fqdn_hostname,
reject_invalid_hostname,
reject_rbl_client list.dsbl.org,
reject_rbl_client relays.ordb.org,
reject_rbl_client bl.spamcop.net,
check_sender_access dbm:$config_directory/spammers
check_sender_access dbm:$config_directory/junk
check_sender_access dbm:$config_directory/freemail_access,
reject_unauth_pipeliningcheck_sender_access type:table

# End of new

I am trying to add some additional restrictions that will not impact
the inbound/outbound emails.

Does anyone know what can be SAFELY added to this file to kick out
spammers?

I pulled this info from a website will any of these ?

check_sender_access type:table
check_sender_mx_access type:table
check_sender_ns_access type:table
reject_authenticated_sender_login_mismatch
reject_sender_login_mismatch
reject_unknown_sender_domain
reject_unlisted_sender
reject_unverified_sender

thanks