Sendmail Installation Guide Installation Guide

Sendmail is a free and open-source Mail Server. A general purpose internetwork email routing facility

Hardware Requirements:

CPU: 2 cores minimum (4+ cores recommended)

RAM: 2GB minimum (4GB+ recommended)

Storage: 1GB for installation

Network: 25/587 ports

Operating System:

Linux: Any modern distribution (RHEL, Debian, Ubuntu, CentOS, Fedora, Arch, Alpine, openSUSE)

macOS: 10.14+ (Mojave or newer)

Windows: Windows Server 2016+ or Windows 10

FreeBSD: 11.0+

Network Requirements:

Port 25/587 (default sendmail port)

Dependencies:

sendmail-cf, m4

System Access: root or sudo privileges required

This guide supports installation on:

RHEL 8/9 and derivatives (CentOS Stream, Rocky Linux, AlmaLinux)

Debian 11/12

Ubuntu 20.04/22.04/24.04 LTS

Arch Linux (rolling release)

Alpine Linux 3.18+

openSUSE Leap 15.5+ / Tumbleweed

SUSE Linux Enterprise Server (SLES) 15+

macOS 12+ (Monterey and later)

FreeBSD 13+

Windows 10/11/Server 2019+ (where applicable)

bash

# Install EPEL repository if needed
sudo dnf install -y epel-release

# Install sendmail
sudo dnf install -y sendmail sendmail-cf, m4

# Enable and start service
sudo systemctl enable --now sendmail

# Configure firewall
sudo firewall-cmd --permanent --add-service=sendmail
sudo firewall-cmd --reload

# Verify installation
sendmail --version || systemctl status sendmail

bash

# Update package index
sudo apt update

# Install sendmail
sudo apt install -y sendmail sendmail-cf, m4

# Enable and start service
sudo systemctl enable --now sendmail

# Configure firewall
sudo ufw allow 25/587

# Verify installation
sendmail --version || systemctl status sendmail

bash

# Install sendmail
sudo pacman -S sendmail

# Enable and start service
sudo systemctl enable --now sendmail

# Verify installation
sendmail --version || systemctl status sendmail

bash

# Install sendmail
apk add --no-cache sendmail

# Enable and start service
rc-update add sendmail default
rc-service sendmail start

# Verify installation
sendmail --version || rc-service sendmail status

bash

# Install sendmail
sudo zypper install -y sendmail sendmail-cf, m4

# Enable and start service
sudo systemctl enable --now sendmail

# Configure firewall
sudo firewall-cmd --permanent --add-service=sendmail
sudo firewall-cmd --reload

# Verify installation
sendmail --version || systemctl status sendmail

bash

# Using Homebrew
brew install sendmail

# Start service
brew services start sendmail

# Verify installation
sendmail --version

bash

# Using pkg
pkg install sendmail

# Enable in rc.conf
echo 'sendmail_enable="YES"' >> /etc/rc.conf

# Start service
service sendmail start

# Verify installation
sendmail --version || service sendmail status

powershell

# Using Chocolatey
choco install sendmail

# Or using Scoop
scoop install sendmail

# Verify installation
sendmail --version

bash

# Create configuration directory if needed
sudo mkdir -p /etc/mail

# Set up basic configuration
sudo tee /etc/mail/sendmail.conf << 'EOF'
# Sendmail Configuration
MaxDaemonChildren=100
EOF

# Test configuration
sudo sendmail -t || sudo sendmail configtest

# Reload service
sudo systemctl reload sendmail

bash

# Set appropriate permissions
sudo chown -R sendmail:sendmail /etc/mail
sudo chmod 750 /etc/mail

# Enable security features
# See security section for detailed hardening steps

bash

# Enable service
sudo systemctl enable sendmail

# Start service
sudo systemctl start sendmail

# Stop service
sudo systemctl stop sendmail

# Restart service
sudo systemctl restart sendmail

# Reload configuration
sudo systemctl reload sendmail

# Check status
sudo systemctl status sendmail

# View logs
sudo journalctl -u sendmail -f

bash

# Enable service
rc-update add sendmail default

# Start service
rc-service sendmail start

# Stop service
rc-service sendmail stop

# Restart service
rc-service sendmail restart

# Check status
rc-service sendmail status

bash

# Enable in /etc/rc.conf
echo 'sendmail_enable="YES"' >> /etc/rc.conf

# Start service
service sendmail start

# Stop service
service sendmail stop

# Restart service
service sendmail restart

# Check status
service sendmail status

bash

# Using Homebrew services
brew services start sendmail
brew services stop sendmail
brew services restart sendmail

# Check status
brew services list | grep sendmail

powershell

# Start service
net start sendmail

# Stop service
net stop sendmail

# Using PowerShell
Start-Service sendmail
Stop-Service sendmail
Restart-Service sendmail

# Check status
Get-Service sendmail

bash

# Configure performance settings
cat >> /etc/mail/sendmail.conf << 'EOF'
MaxDaemonChildren=100
EOF

# Apply system tuning
sudo sysctl -w net.core.somaxconn=65535
sudo sysctl -w net.ipv4.tcp_max_syn_backlog=65535

# Restart service
sudo systemctl restart sendmail

bash

# Configure clustering (if supported)
# See official documentation for cluster setup

# Basic load balancing setup example
# Configure multiple instances on different ports

nginx

upstream sendmail_backend {
    server 127.0.0.1:25/587;
    server 127.0.0.1:{default_port}1 backup;
}

server {
    listen 80;
    server_name sendmail.example.com;
    return 301 https://$server_name$request_uri;
}

server {
    listen 443 ssl http2;
    server_name sendmail.example.com;

    ssl_certificate /etc/ssl/certs/sendmail.example.com.crt;
    ssl_certificate_key /etc/ssl/private/sendmail.example.com.key;

    location / {
        proxy_pass http://sendmail_backend;
        proxy_set_header Host $host;
        proxy_set_header X-Real-IP $remote_addr;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
        proxy_set_header X-Forwarded-Proto $scheme;
        
        # WebSocket support (if needed)
        proxy_http_version 1.1;
        proxy_set_header Upgrade $http_upgrade;
        proxy_set_header Connection "upgrade";
    }
}

apache

<VirtualHost *:80>
    ServerName sendmail.example.com
    Redirect permanent / https://sendmail.example.com/
</VirtualHost>

<VirtualHost *:443>
    ServerName sendmail.example.com
    
    SSLEngine on
    SSLCertificateFile /etc/ssl/certs/sendmail.example.com.crt
    SSLCertificateKeyFile /etc/ssl/private/sendmail.example.com.key
    
    ProxyRequests Off
    ProxyPreserveHost On
    
    ProxyPass / http://127.0.0.1:25/587/
    ProxyPassReverse / http://127.0.0.1:25/587/
    
    # WebSocket support (if needed)
    RewriteEngine on
    RewriteCond %{HTTP:Upgrade} websocket [NC]
    RewriteCond %{HTTP:Connection} upgrade [NC]
    RewriteRule ^/?(.*) "ws://127.0.0.1:25/587/$1" [P,L]
</VirtualHost>

haproxy

frontend sendmail_frontend
    bind *:80
    bind *:443 ssl crt /etc/ssl/certs/sendmail.pem
    redirect scheme https if !{ ssl_fc }
    default_backend sendmail_backend

backend sendmail_backend
    balance roundrobin
    option httpchk GET /health
    server sendmail1 127.0.0.1:25/587 check
    server sendmail2 127.0.0.1:{default_port}1 check backup

bash

# Set appropriate permissions
sudo chown -R sendmail:sendmail /etc/mail
sudo chmod 750 /etc/mail

# Configure firewall
sudo firewall-cmd --permanent --add-service=sendmail
sudo firewall-cmd --reload

# Enable SELinux policies (if applicable)
sudo setsebool -P httpd_can_network_connect on

# Configure fail2ban
sudo tee /etc/fail2ban/jail.d/sendmail.conf << 'EOF'
[sendmail]
enabled = true
port = 25/587
filter = sendmail
logpath = /var/log/mail/*.log
maxretry = 5
bantime = 3600
EOF

bash

# Generate SSL certificates
sudo openssl req -x509 -nodes -days 365 -newkey rsa:2048 \
    -keyout /etc/ssl/private/sendmail.key \
    -out /etc/ssl/certs/sendmail.crt

# Configure SSL in sendmail
# See official documentation for SSL configuration

PostgreSQL Backend (if applicable)

bash

# Create database and user
sudo -u postgres psql << EOF
CREATE DATABASE sendmail_db;
CREATE USER sendmail_user WITH ENCRYPTED PASSWORD 'secure_password';
GRANT ALL PRIVILEGES ON DATABASE sendmail_db TO sendmail_user;
EOF

# Configure sendmail to use PostgreSQL
# See official documentation for database configuration

bash

# Create database and user
sudo mysql << EOF
CREATE DATABASE sendmail_db;
CREATE USER 'sendmail_user'@'localhost' IDENTIFIED BY 'secure_password';
GRANT ALL PRIVILEGES ON sendmail_db.* TO 'sendmail_user'@'localhost';
FLUSH PRIVILEGES;
EOF

bash

# Kernel parameters
sudo tee -a /etc/sysctl.conf << EOF
net.core.somaxconn = 65535
net.ipv4.tcp_max_syn_backlog = 65535
net.ipv4.ip_local_port_range = 1024 65535
net.core.netdev_max_backlog = 5000
vm.swappiness = 10
EOF

sudo sysctl -p

# Sendmail specific tuning
MaxDaemonChildren=100

bash

# Configure system limits
sudo tee -a /etc/security/limits.conf << EOF
sendmail soft nofile 65535
sendmail hard nofile 65535
sendmail soft nproc 32768
sendmail hard nproc 32768
EOF

yaml

# prometheus.yml configuration
scrape_configs:
  - job_name: 'sendmail'
    static_configs:
      - targets: ['localhost:25/587']
    metrics_path: '/metrics'

bash

# Basic health check script
#!/bin/bash
if systemctl is-active --quiet sendmail; then
    echo "Sendmail is running"
    exit 0
else
    echo "Sendmail is not running"
    exit 1
fi

bash

# Configure log rotation
sudo tee /etc/logrotate.d/sendmail << 'EOF'
/var/log/mail/*.log {
    daily
    rotate 14
    compress
    delaycompress
    missingok
    notifempty
    create 0640 sendmail sendmail
    postrotate
        systemctl reload sendmail > /dev/null 2>&1 || true
    endscript
}
EOF

bash

#!/bin/bash
# Sendmail backup script
BACKUP_DIR="/backup/sendmail"
DATE=$(date +%Y%m%d_%H%M%S)

mkdir -p "$BACKUP_DIR"

# Stop service (if required)
systemctl stop sendmail

# Backup configuration
tar -czf "$BACKUP_DIR/sendmail-config-$DATE.tar.gz" /etc/mail

# Backup data (adjust paths as needed)
tar -czf "$BACKUP_DIR/sendmail-data-$DATE.tar.gz" /var/lib/sendmail

# Start service
systemctl start sendmail

# Clean old backups (keep 30 days)
find "$BACKUP_DIR" -name "*.tar.gz" -mtime +30 -delete

echo "Backup completed: $BACKUP_DIR"

bash

# Stop service
sudo systemctl stop sendmail

# Restore configuration
sudo tar -xzf /backup/sendmail/sendmail-config-*.tar.gz -C /

# Restore data
sudo tar -xzf /backup/sendmail/sendmail-data-*.tar.gz -C /

# Set permissions
sudo chown -R sendmail:sendmail /etc/mail
sudo chown -R sendmail:sendmail /var/lib/sendmail

# Start service
sudo systemctl start sendmail

1. Service won't start:

bash

# Check logs
sudo journalctl -u sendmail -n 100
sudo tail -f /var/log/mail/*.log

# Check configuration
sudo sendmail -t || sudo sendmail configtest

# Check permissions
ls -la /etc/mail
ls -la /var/lib/sendmail

2. Connection refused:

bash

# Check if service is listening
sudo ss -tlnp | grep 25/587
sudo netstat -tlnp | grep 25/587

# Check firewall
sudo firewall-cmd --list-all
sudo iptables -L -n

# Test connection
telnet localhost 25/587
nc -zv localhost 25/587

3. Performance issues:

bash

# Check resource usage
top -p $(pgrep sendmail)
htop -p $(pgrep sendmail)

# Check connections
ss -ant | grep :25/587 | wc -l

# Monitor I/O
iotop -p $(pgrep sendmail)

bash

# Run in debug mode
sudo sendmail -d
# or
sudo sendmail debug

# Increase log verbosity
# Edit configuration to enable debug logging

yaml

version: '3.8'
services:
  sendmail:
    image: sendmail:latest
    container_name: sendmail
    ports:
      - "25/587:25/587"
    volumes:
      - ./config:/etc/mail
      - ./data:/var/lib/sendmail
    environment:
      - sendmail_CONFIG=/etc/mail/sendmail.conf
    restart: unless-stopped
    networks:
      - sendmail_net

networks:
  sendmail_net:
    driver: bridge

yaml

apiVersion: apps/v1
kind: Deployment
metadata:
  name: sendmail
spec:
  replicas: 3
  selector:
    matchLabels:
      app: sendmail
  template:
    metadata:
      labels:
        app: sendmail
    spec:
      containers:
      - name: sendmail
        image: sendmail:latest
        ports:
        - containerPort: 25/587
        volumeMounts:
        - name: config
          mountPath: /etc/mail
      volumes:
      - name: config
        configMap:
          name: sendmail-config
---
apiVersion: v1
kind: Service
metadata:
  name: sendmail
spec:
  selector:
    app: sendmail
  ports:
  - port: 25/587
    targetPort: 25/587
  type: LoadBalancer

yaml

---
- name: Install and configure Sendmail
  hosts: all
  become: yes
  tasks:
    - name: Install sendmail
      package:
        name: sendmail
        state: present
    
    - name: Configure sendmail
      template:
        src: sendmail.conf.j2
        dest: /etc/mail/sendmail.conf
        owner: sendmail
        group: sendmail
        mode: '0640'
      notify: restart sendmail
    
    - name: Start and enable sendmail
      systemd:
        name: sendmail
        state: started
        enabled: yes
  
  handlers:
    - name: restart sendmail
      systemd:
        name: sendmail
        state: restarted

Maintenance

bash

# RHEL/CentOS/Rocky/AlmaLinux
sudo dnf update sendmail

# Debian/Ubuntu
sudo apt update && sudo apt upgrade sendmail

# Arch Linux
sudo pacman -Syu sendmail

# Alpine Linux
apk update && apk upgrade sendmail

# openSUSE
sudo zypper update sendmail

# FreeBSD
pkg update && pkg upgrade sendmail

# Always backup before updates
tar -czf /backup/sendmail-pre-update-$(date +%Y%m%d).tar.gz /etc/mail

# Restart after updates
sudo systemctl restart sendmail

Regular Maintenance Tasks

bash

# Clean logs
find /var/log/mail -name "*.log" -mtime +30 -delete

# Verify integrity
sudo sendmail --verify || sudo sendmail check

# Update databases (if applicable)
sudo sendmail-update-db

# Optimize performance
sudo sendmail-optimize

# Check for security updates
sudo sendmail --security-check

Official Documentation: https://docs.sendmail.org/

GitHub Repository: https://github.com/sendmail/sendmail

Community Forum: https://forum.sendmail.org/

Wiki: https://wiki.sendmail.org/

Comparison vs Postfix, Exim, Qmail, OpenSMTPD: https://docs.sendmail.org/comparison

---

Note: This guide is part of the HowToMgr collection. Always refer to official documentation for the most up-to-date information.

1. Prerequisites

2. Supported Operating Systems

3. Installation

RHEL/CentOS/Rocky Linux/AlmaLinux

Debian/Ubuntu

Arch Linux

Alpine Linux

openSUSE/SLES

macOS

FreeBSD

Windows

Initial Configuration

Basic Configuration

Security Hardening

5. Service Management

systemd (RHEL, Debian, Ubuntu, Arch, openSUSE)

OpenRC (Alpine Linux)

rc.d (FreeBSD)

launchd (macOS)

Windows Service Manager

Advanced Configuration

Performance Optimization

Clustering and High Availability

Reverse Proxy Setup

nginx Configuration

Apache Configuration

HAProxy Configuration

Security Configuration

Basic Security Setup

SSL/TLS Configuration

Database Setup

PostgreSQL Backend (if applicable)

MySQL/MariaDB Backend (if applicable)

Performance Optimization

System Tuning

Resource Limits

Monitoring

Prometheus Integration

Health Checks

Log Monitoring

9. Backup and Restore

Backup Script

Restore Procedure

6. Troubleshooting

Common Issues

Debug Mode

Integration Examples

Docker Compose

Kubernetes Deployment

Ansible Playbook

Maintenance

Update Procedures

Regular Maintenance Tasks

Additional Resources

Related Mail servers Guides

Dovecot Installation Guide

Exim Installation Guide

Haraka Installation Guide