How to Block Spam on Server

Prerequisites

Before blocking spam, make sure you have:

• SSH access to your VPS
• Root or sudo privileges
• Postfix or other MTA installed

Method 1: Install and Configure SpamAssassin

Connect to your VPS:

ssh hxroot@YOUR_SERVER_IP -p 22

sudo apt install spamassassin spamc -y
sudo systemctl enable spamassassin
sudo systemctl start spamassassin

Configure Postfix to use SpamAssassin by editing /etc/postfix/master.cf.

Method 2: Use RBLs (Realtime Blackhole Lists) in Postfix

Edit /etc/postfix/main.cf:

smtpd_recipient_restrictions = permit_mynetworks,
    reject_rbl_client zen.spamhaus.org,
    reject_rbl_client bl.spamcop.net,
    permit

Restart Postfix:

sudo systemctl restart postfix

Method 3: Configure Greylisting with postgrey

sudo apt install postgrey -y
sudo systemctl enable postgrey
sudo systemctl start postgrey

In Postfix main.cf add:

smtpd_recipient_restrictions = check_policy_service inet:127.0.0.1:10023

Method 4: Block Common Spam Domains

sudo nano /etc/postfix/access

.spammerdomain.com REJECT
.bad.net REJECT

Create database:

sudo postmap /etc/postfix/access

Method 5: Limit Incoming Email Volume (Rate Limiting)

Add to main.cf:

smtpd_client_message_rate_limit = 10
smtpd_client_recipient_rate_limit = 10
anvil_rate_time_unit = 60s

Method 6: Use Fail2ban for Postfix (Ban abusive IPs)

Create jail in /etc/fail2ban/jail.local:

[postfix]
enabled = true
logpath = /var/log/mail.log
maxretry = 5
bantime = 3600

Restart Fail2ban.