Skip to content

mb-milter Service

Milter protocol interface for Postfix integration providing real-time SMTP filtering.

Overview

mb-milter implements the Postfix milter (mail filter) protocol for real-time email filtering during SMTP conversation. Provides:

  • SMTP-time filtering - Block before DATA phase
  • Header modification - Add/remove headers
  • Recipient validation - Real-time recipient checks
  • Connection filtering - IP-based blocking
  • Greylisting - Temporary rejection for spam prevention

Operates on port 10032 and interfaces with Postfix milter protocol.

Architecture

Milter protocol allows filtering at multiple SMTP stages:

SMTP Connection
  ↓ CONNECT stage (IP check)
mb-milter: GeoIP, IP blacklist
  ↓ HELO stage
mb-milter: HELO validation
  ↓ MAIL FROM stage
mb-milter: Sender validation, SPF check
  ↓ RCPT TO stage
mb-milter: Recipient validation, greylisting
  ↓ DATA stage
mb-milter: Header checks
  ↓ END-OF-MESSAGE
[mb-filter takes over for content filtering]

Configuration

Service File

Location: /etc/systemd/system/mb-milter.service

[Unit]
Description=Mailborder Milter Interface
After=network.target mb-rpcd.service
Requires=mb-rpcd.service

[Service]
Type=forking
User=mailborder
Group=mailborder
ExecStart=/usr/libexec/mailborder/php_enc/mb-milter start
ExecStop=/usr/libexec/mailborder/php_enc/mb-milter stop
PIDFile=/var/run/mailborder/mb-milter.pid
Restart=always
RestartSec=10

[Install]
WantedBy=multi-user.target

Postfix Integration

/etc/postfix/main.cf: 

smtpd_milters = inet:127.0.0.1:10032
non_smtpd_milters = $smtpd_milters
milter_default_action = accept
milter_protocol = 6

Reload Postfix: 

sudo postfix reload

Milter Settings

# Enable/disable features
sudo mb-config set milter.geoip_check true
sudo mb-config set milter.greylist_enabled true
sudo mb-config set milter.recipient_validation true

# Greylisting delay
sudo mb-config set milter.greylist_delay 300  # 5 minutes

# Apply changes
sudo systemctl reload mb-milter

Operations

Start: 

sudo systemctl start mb-milter

Status: 

sudo systemctl status mb-milter

Logs: 

sudo tail -f /var/log/mailborder/mb-milter.log

See Also