Sendmail security

Sendmail security

Sendmail security 150 150 Roderick Derks

Adding some hints here to secure your mailserver. The list will grow in time. 

$ vi /etc/mail/access

# Description showing bellow for the format of this file comes from
# the Sendmail source distribution under “cf/README” file.
#
# The table itself uses e-mail addresses, domain names, and network
# numbers as keys. For example,
#
#        spammer@aol.com                REJECT
#        cyberspammer.com               REJECT
#        192.168.212                            REJECT
#
# would refuse mail from spammer@aol.com, any user from cyberspammer.com
# (or any host within the cyberspammer.com domain), and any host on the
# 192.168.212.* network.
#
# The value part of the map can contain:
#
#        OK           Accept mail even if other rules in the
#                        running ruleset would reject it, for example,
#                        if the domain name is unresolvable.
#        RELAY   Accept mail addressed to the indicated domain or
#                        received from the indicated domain for relaying
#                        through your SMTP server.  RELAY also serves as
#                        an implicit OK for the other checks.
#        REJECT  Reject the sender or recipient with a general
#                        purpose message.
#        DISCARD    Discard the message completely using the
#                        $#discard mailer.  This only works for sender
#                        addresses (i.e., it indicates that you should
#                        discard anything received from the indicated
#                        domain).
#        ### any text    where ### is an RFC 821 compliant error code
#                        and “any text” is a message to return for
#                        the command.
#
# For example:
#
#        cyberspammer.com        550 We don’t accept mail from spammers
#        okay.cyberspammer.com          OK
#        sendmail.org                           OK
#        128.32                                 RELAY
#
# would accept mail from okay.cyberspammer.com, but would reject mail
# from all other hosts at cyberspammer.com with the indicated message.
# It would allow accept mail from any hosts in the sendmail.org domain,
# and allow relaying for the 128.32.*.* network.
#
# You can also use the access database to block sender addresses based on
# the username portion of the address. For example:
#
#        FREE.STEALTH.MAILER@    550 Spam not accepted
#
# Note that you must include the @ after the username to signify that
# this database entry is for checking only the username portion of the
# sender address.
#
# If you use like we do in our “sendmail.mc macro configuration:
#
#        FEATURE(`blacklist_recipients’)
#
# then you can add entries to the map for local users, hosts in your
# domains, or addresses in your domain which should not receive mail:
#
#        badlocaluser            550 Mailbox disabled for this username
#        host.mydomain.com       550 That host does not accept mail
#        user@otherhost.mydomain.com     550 Mailbox disabled for this recipient
#
# This would prevent a recipient of badlocaluser@mydomain.com, any
# user at host.mydomain.com, and the single address
# user@otherhost.mydomain.com from receiving mail. Enabling this
# feature will keep you from sending mails to all addresses that
# have an error message or REJECT as value part in the access map.
# Taking the example from above:
#
#        spammer@aol.com                REJECT
#        cyberspammer.com               REJECT
#
# Mail can’t be sent to spammer@aol.com or anyone at cyberspammer.com.
#
# Now our configuration of access file,
# by default we allow relaying from localhost…
localhost.localdomain           RELAY
localhost                               RELAY
127.0.0.1                               RELAY
192.168.1                               RELAY

$ service sendmail reload 

Roderick Derks

Liefhebber van fietsen, van het oplossen van IT puzzels, en van het delen van informatie om anderen te helpen.

All stories by:Roderick Derks

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