How to Set Up Mailcow: Dockerized Email Server on Contabo VPS (Self-Hosted Guide)

The Financial Burden of Enterprise Email SaaS

Google Workspace and Microsoft 365 charge between $7.20 and $18 per user per month. For a growing agency or business with 25 employees and several domain aliases, email licensing alone costs upwards of $2,000 to $5,000 annually. By deploying Mailcow: Dockerized on a high-RAM Contabo Cloud VPS, you can host thousands of mailboxes with enterprise spam filtering, modern webmail, and full data sovereignty for just $8.50 per month.

Server Requirements and Choosing the Right Contabo Tier

Mailcow is an enterprise-grade suite comprising Postfix, Dovecot, Nginx, MariaDB, Redis, Rspamd (spam filtering), and ClamAV (antivirus scanning). ClamAV alone requires at least 4 GB of RAM to hold virus signature databases in memory:

• Recommended VPS: Contabo Cloud VPS 2 (6 vCPU cores, 16 GB RAM, 100 GB NVMe).
• Operating System: Clean installation of Ubuntu 24.04 LTS.
• Clean IP Address: Verify your allocated IP is not on Spamhaus or Barracuda blacklists.

Step 1: Setting Up Reverse DNS (rDNS / PTR Record)

Receiving mail servers (Gmail, Outlook, Yahoo) reject incoming emails if the sending server's IP does not resolve back to its Fully Qualified Domain Name (FQDN). On Contabo:

1. Log in to the Contabo Customer Control Panel (CCP).
2. Navigate to IP Management -> Reverse DNS.
3. Locate your VPS IPv4 address and set the PTR value to your mail hostname (e.g. mail.yourdomain.com).
4. Save changes and allow 1 hour for global DNS propagation.

Step 2: Configuring DNS Records at Your Registrar

Add the following mandatory records to your domain's DNS zone:

# Mail Host A Record
mail.yourdomain.com.    IN A        YOUR_CONTABO_IP

# Primary MX Record
yourdomain.com.         IN MX 10    mail.yourdomain.com.

# Autodiscover & Autoconfig for Outlook / Thunderbird
autodiscover.yourdomain.com. IN CNAME mail.yourdomain.com.
autoconfig.yourdomain.com.   IN CNAME mail.yourdomain.com.

# Sender Policy Framework (SPF)
yourdomain.com.         IN TXT      "v=spf1 mx a:mail.yourdomain.com ~all"

# DMARC Policy
_dmarc.yourdomain.com.  IN TXT      "v=DMARC1; p=quarantine; rua=mailto:dmarc@yourdomain.com"

Step 3: Installing Docker & Git Dependencies

Connect to your Contabo VPS via SSH and prepare the host:

sudo apt update && sudo apt upgrade -y
sudo apt install -y curl git apt-transport-https ca-certificates gnupg

# Install Docker CE
curl -fsSL https://get.docker.com -o get-docker.sh
sudo sh get-docker.sh
sudo systemctl enable --now docker

Step 4: Cloning Mailcow and Generating Configuration

Mailcow lives in /opt/mailcow-dockerized:

cd /opt
sudo git clone https://github.com/mailcow/mailcow-dockerized
cd mailcow-dockerized

# Run the interactive configuration generator
sudo ./generate_config.sh

During the script execution, enter:

• Mail server hostname: mail.yourdomain.com
• Timezone: UTC or your local timezone
• Branch: master

Step 5: Pulling Images and Launching the Stack

Download the container images and launch Mailcow in background mode:

sudo docker compose pull
sudo docker compose up -d

Inspect the running containers to verify health status:

sudo docker compose ps

Step 6: Logging in to Mailcow Admin & Activating DKIM

1. Open your browser and navigate to https://mail.yourdomain.com.
2. Log in using default credentials: Username admin, Password moohoo (change immediately under Administrator settings).
3. Go to Configuration -> Mail Setup -> Domains and click Add Domain.
4. Under the DKIM tab, generate a 2048-bit DKIM key for your domain.
5. Copy the public key value and publish it as a TXT record at dkim._domainkey.yourdomain.com.

Step 7: Testing Deliverability

Create a test mailbox, log in to SOGo webmail at https://mail.yourdomain.com/SOGo, and send a test message to mail-tester.com. With SPF, DKIM, DMARC, and Contabo's rDNS aligned, you will achieve a perfect 10/10 score.

Frequently Asked Questions (FAQ)

Does Contabo block port 25?

On new accounts, Contabo sometimes blocks outbound port 25 to prevent spam abuse. Simply open a quick ticket with Contabo support stating you are running a private business mail server; their team unblocks port 25 promptly once identity is verified.