Introduction

Email remains a cornerstone of contemporary communication. Whether for professional notifications or personal correspondence, maintaining a robust and dependable mail server is crucial. Although cloud-based solutions dominate the market, self-hosting a mail server offers control, customization, and educational opportunities that managed services cannot provide.

This guide will walk you through setting up a secure and efficient mail server using Dovecot on an Ubuntu Server. Dovecot is a lightweight and high-performance IMAP and POP3 server that ensures secure access to mailboxes. When combined with Postfix, it forms a powerful mail server stack capable of sending and receiving messages seamlessly.

Regardless of whether you're a system administrator, a DevOps enthusiast, or simply interested in managing your own mail infrastructure, this article offers a comprehensive exploration of configuring Dovecot on Ubuntu.

Prerequisites

Before proceeding with the configuration and deployment, make sure the following prerequisites are fulfilled:

• Ubuntu Server (version 20.04 or later recommended)

• Root or sudo access

• Static IP address assigned to your server

• Fully Qualified Domain Name (FQDN) pointing to your server

• Proper DNS records:

  • An A record linking your domain to your server's IP address
  • An MX record directing mail traffic to your mail server’s FQDN
  • Optionally: SPF, DKIM, and DMARC records for enhanced email authentication

Additionally, ensure your system is updated:

sudo apt update && sudo apt upgrade -y

Understanding the Mail Server Stack

A modern mail server consists of multiple components:

• Postfix: The SMTP server responsible for sending and routing outgoing mail.
• Dovecot: Manages the retrieval of mail via IMAP/POP3 and secure authentication.
• SpamAssassin / ClamAV: Filters spam and detects malware.
• TLS/SSL: Ensures encrypted communication channels.

Here's how these components interact:

1. Postfix receives emails from external sources.
2. It stores incoming messages in local mailboxes.
3. Dovecot allows users to access their mail securely using IMAP or POP3.
4. TLS/SSL encryption secures the entire process, protecting privacy.

Step 1: Installing Postfix and Dovecot

Install Postfix:

sudo apt install postfix -y

During installation, you’ll be prompted to select a configuration. Choose:

• General type of mail configuration: Internet Site
• System mail name: yourdomain.com

If needed, you can reconfigure it later:

sudo dpkg-reconfigure postfix

Install Dovecot:

sudo apt install dovecot-core dovecot-imapd dovecot-pop3d -y

Step 2: Configuring Mail Directories

We'll use the Maildir format, which stores each message in a separate file, simplifying management.

Update Postfix to deliver to Maildir:

Edit /etc/postfix/main.cf and add:

home_mailbox = Maildir/

Then reload Postfix:

sudo systemctl restart postfix

For each user, create a Maildir:

sudo mkdir /home/username/Maildir sudo maildirmake.dovecot /home/username/Maildir sudo chown -R username:username /home/username/Maildir

Step 3: Configuring Dovecot

Dovecot’s configuration files are located in /etc/dovecot/. The main file is dovecot.conf.

Mail Location Edit /etc/dovecot/conf.d/10-mail.conf:

mail_location = maildir:~/Maildir

Ensure mail user privileges:

first_valid_uid = 1000

Authentication Configuration Edit /etc/dovecot/conf.d/10-auth.conf:

disable_plaintext_auth = yes auth_mechanisms = plain login

Use system users for authentication:

!include auth-system.conf.ext

Configure Services Edit /etc/dovecot/conf.d/10-master.conf and enable the following section under service auth:

unix_listener /var/spool/postfix/private/auth { mode = 0660 user = postfix group = postfix }

Restart Dovecot:

sudo systemctl restart dovecot

Step 4: Enabling SSL/TLS Encryption

For production environments, consider using Let’s Encrypt. For testing purposes, create a self-signed certificate:

sudo openssl req -new -x509 -days 365 -nodes -out /etc/ssl/certs/mailcert.pem -keyout /etc/ssl/private/mailkey.pem

Edit /etc/dovecot/conf.d/10-ssl.conf:

ssl = required ssl_cert = /ssl/certs/mailcert.pem ssl_key = /ssl/private/mailkey.pem

Restart Dovecot again:

sudo systemctl restart dovecot

Step 5: Configuring the Firewall

Open necessary ports:

sudo ufw allow 25,587,110,995,143,993/tcp sudo ufw enable

Common ports:

• 25: SMTP
• 587: Submission (SMTP with auth)
• 110: POP3
• 995: POP3S
• 143: IMAP
• 993: IMAPS

Step 6: Adding Mail Users

To add local users:

sudo adduser mailuser

Create mail directories:

sudo mkdir /home/mailuser/Maildir sudo maildirmake.dovecot /home/mailuser/Maildir sudo chown -R mailuser:mailuser /home/mailuser/Maildir

These users can now connect using an email client via IMAP or POP3.

Step 7: Testing the Mail Server

Use openssl to test IMAPS:

openssl s_client -connect yourdomain.com:993

You can also use telnet to check connections or configure a mail client like Thunderbird:

• Incoming: IMAP, port 993, SSL/TLS, normal password
• Outgoing: SMTP, port 587, STARTTLS, normal password

Check logs for errors:

sudo tail -f /var/log/mail.log

Step 8: Hardening and Maintenance

Enable Fail2Ban:

sudo apt install fail2ban -y

Fail2Ban monitors logs and bans IPs showing signs of malicious activity.

Regular Updates Set up unattended upgrades:

sudo apt install unattended-upgrades

Mail Backup Backup /etc/postfix, /etc/dovecot, and mailboxes (typically under /home/*/Maildir or /var/mail).

You may use rsnapshot or rsync for daily incremental backups.

Conclusion

Following this guide, you’ve built a fully functional and secure mail server using Postfix and Dovecot on Ubuntu. You now possess:

• A working SMTP server for sending mail.
• A Dovecot-based IMAP/POP3 server for accessing messages.
• SSL/TLS secured communication.
• Local users capable of sending and receiving emails from mail clients.

With fine-tuned configurations and proper security measures, your mail server is prepared for practical use. You can further enhance your setup by integrating webmail clients like Roundcube, enabling spam filtering, and setting up email authentication (SPF, DKIM, DMARC).

The above is the detailed content of Setting Up a Secure Mail Server with Dovecot on Ubuntu Server. For more information, please follow other related articles on the PHP Chinese website!