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
Configuration
# 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.
See also:
🐧 5 comments so far... add one ↓
| Category | List of Unix and Linux commands |
|---|---|
| File Management | cat |
| Firewall | Alpine Awall • CentOS 8 • OpenSUSE • RHEL 8 • Ubuntu 16.04 • Ubuntu 18.04 • Ubuntu 20.04 |
| Network Utilities | dig • host • ip • nmap |
| OpenVPN | CentOS 7 • CentOS 8 • Debian 10 • Debian 8/9 • Ubuntu 18.04 • Ubuntu 20.04 |
| Package Manager | apk • apt |
| Processes Management | bg • chroot • cron • disown • fg • jobs • killall • kill • pidof • pstree • pwdx • time |
| Searching | grep • whereis • which |
| User Information | groups • id • lastcomm • last • lid/libuser-lid • logname • members • users • whoami • who • w |
| WireGuard VPN | Alpine • CentOS 8 • Debian 10 • Firewall • Ubuntu 20.04 |
how can i block example@* or example*@* in sendmail access databse?
nice , I use to love cyberciti , great for linux ppl
Thanks again :)
good reference material
Hi Guys
I am using Centos and sendmail, how do i block all outgoing emails and allow only email from my domain