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Meer
10-10-2010, 07:18 PM
Q. How do I block some1@domain.com or IP address for Sendmail spammers?
A. Sendmail offers various options to block an email address, domain name or IP address using access database.
File /etc/mail/access act as an access control for your Sendmail smtp server. With this file you can define:


Who we accept mail from
Who we accept relaying from
Who we will not send to etc

Configuratio

n
# vi /etc/mail/sendmail.cf

Make sure following line exists in your configuration file (otherwise you need to add/append following line):
FEATURE(`access_db')dnl
Save the file and exit to shell prompt. Now, open /etc/mail/access file:

# vi /etc/mail/access
To block junk or spam mail use following format
spam@domain.com REJECT
192.168.1.100 REJECT
202.54.1.100/255.0.0.0 REJECT
Save the file. Once sendmail.mc or access file is modified, you need to regenerate /etc/mail/sendmail.cf or rebuild the access database. Type any one of the following commands:

# cd /etc/mail

# make
OR

# m4 /etc/mail/sendmail.mc > /etc/mail/sendmail.cf
Restart the sendmail:

# /etc/init.d/sendmail restart
Other options supported by access database


OK - Accept email FROM: or TO: specified address
DISCARD - Do not accept email FROM: or TO: specified address
REJECT - Drop email with an error FROM: or TO: specified address
HATER - Use check_mail and check_realy rules for email
FRIEND - Do not use check_mail and check_realy rules for email
ERROR:ecode:etext - Drop email with specified error code (ecode) and error text message (etext).

Examples
abc.com ERROR:550:Relay denied
FROM:mail@fack.net REJECT
TO:foo@bar.com REJECT
Spam:abuse@ FRIEND
Connect:202.54.1.1 ERROR:5.7.1:550: Relay denied
How do I test access database is working or not?
Use sendmail with -bt option as follows:

# sendmail –bt
> check_mail user@abc.com
OR use telnet command:

# telnet localhost 25
HELO localhost
MAIL FROM:user@abc.com
In both case you should get relay denied error.