Blocking Spam - The access File
The access file offers you the ability to block incoming E-mail messages based on the E-mail
address or sending domain of the incoming message. Some specific options you can chose include the
following.
- Reject e-mail from specific users, domains, IP addresses, and networks.
- Specify the text (or use sendmail's default) of messages to return to senders of rejected e-mail.
- Accept e-mail from specific users within a domain, while rejecting e-mail from all other senders in the domain.
- Reject e-mail sent to specific local users.
There are also a number of other features of the access file, which are documented in the /usr/share/sendmail/cf/README file.
The access file settings are already built in to your VPS sendmail configuration. In order to use them, however, you must first create an access.db file in your /etc/mail directory.
The first step in creating your access.db file is to create a plain-text file in your /etc/mail directory named access. This should contain the domain or e-mail account you want to base the filtering on, with a rule. Detailed instructions for using the access file are included in the /usr/share/sendmail/cf/README file, but a few of the more common rules are listed here.
- OK
- Accept mail even if other rules in the running rule set would reject it, for
example, if the domain name is un-resolvable. "Accept" does not mean "relay", but
at most acceptance for local recipients. That is, OK allows less than RELAY.
- 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.
- ERROR:### "any text"
- the Error number should be an RFC 821 compliant error code, and "any text" is
a message to return for the command. The string should be quoted to avoid
surprises, e.g., sendmail may remove spaces otherwise.
The following is an example of a few different possible entries you could have in your
access file.
cyberspammer.com ERROR:550 "We don't accept mail from spammers"
okay.cyberspammer.com OK
sendmail.org RELAY
128.32 RELAY
IPv6:1:2:3:4:5:6:7 RELAY
[127.0.0.3] OK
[IPv6:1:2:3:4:5:6:7:8] OK
After you have created your /etc/mail/access file, you must convert it into a
.db file which sendmail can read. To do this, run the following command
(as root) on your VPS v2
# makemap hash /etc/mail/access < /etc/mail/access
|
