Exim Setup Guide on Linux

Setting up Exim, a popular mail transfer agent (MTA), on Debian can be straightforward with the right steps. Here’s a comprehensive guide to installing and configuring Exim on a Debian system:

Step 1: Install Exim

First, ensure your system packages are up to date. Open a terminal and run the following commands:

sudo apt update
sudo apt upgrade

Now, install Exim:

sudo apt install exim4

Step 2: Basic Configuration

After installation, you need to configure Exim. Debian provides a configuration script for basic setup. To run it:

sudo dpkg-reconfigure exim4-config

You’ll be prompted with several configuration options:

General Type of Mail Configuration:

Internet site; mail is sent and received directly using SMTP: Choose this if your system will handle direct sending and receiving of emails.
Internet site; mail is sent via smarthost: Select this if your server will relay mail through another mail server (like an ISP).
Satellite system; all mail is sent via smarthost: Use this if your server will relay all mail through another server without receiving any.
Local delivery only; not on a network: Choose this for local-only email delivery.

System Mail Name:

This is the domain name used in email addresses. For example, if your server handles email for example.com, use example.com.

IP Addresses to Listen On:

By default, Exim listens on all IP addresses (127.0.0.1; ::1 for local only, 0.0.0.0 for all IPv4 addresses, or :: for all IPv6 addresses). Adjust based on your needs.

Other Destinations for Mail:

These are other domains for which the server should accept mail. By default, it includes the system’s hostname.

Machines to Relay Mail For:

Specify IP addresses or hostnames that your server will relay mail for. Leave blank if none.

DNS Queries for Local Domains:

Usually set to ‘no’ unless you have specific DNS configurations.

Keep Number of DNS-queries Minimal (Dial-on-Demand)?

Choose ‘no’ unless you have a specific reason to minimize DNS queries.

Delivery Method for Local Mail:

Select the default format for local delivery (usually mbox or Maildir).

Split Configuration into Small Files:

Debian allows splitting configuration into smaller files, which is easier to manage in some setups. The default is no.

Step 3: Verify the Configuration

Once you have completed the basic configuration, verify that Exim is working correctly:

sudo systemctl status exim4

You should see that Exim is active and running. If not, start it with:

sudo systemctl start exim4

Step 4: Testing Exim

To test Exim, send a test email from the command line:

echo "This is a test email" | mail -s "Test Email" your-email@example.com

Check the Exim logs for any issues. The logs are typically located at:

/var/log/exim4/mainlog
/var/log/exim4/paniclog
/var/log/exim4/rejectlog

Step 5: Advanced Configuration

For more advanced configurations, you can edit the main Exim configuration file:

sudo nano /etc/exim4/exim4.conf.template

Or, if you chose to split the configuration into smaller files:

sudo nano /etc/exim4/conf.d/

Each file in the conf.d directory corresponds to different parts of Exim’s configuration. You can modify these files to add specific rules, such as spam filtering, virtual domains, and SSL/TLS settings.

Step 6: Enable TLS/SSL (Optional)

To secure your email transactions, configure Exim to use TLS/SSL. Edit the configuration to include your SSL certificate and key:

sudo nano /etc/exim4/exim4.conf.template

Add or modify the following lines under the MAIN_TLS_ENABLE section:

tls_advertise_hosts = *
tls_certificate = /etc/ssl/certs/your_domain_cert.pem
tls_privatekey = /etc/ssl/private/your_domain_key.pem

After making changes, restart Exim:

sudo systemctl restart exim4

Step 7: Configure SPF, DKIM, and DMARC (Optional)

To improve email deliverability and security, configure SPF, DKIM, and DMARC records. These involve DNS records and additional Exim configuration. Detailed steps for each:

SPF: Publish an SPF record in your DNS zone file.

   v=spf1 mx -all

DKIM: Generate DKIM keys and configure Exim to sign outgoing emails.

Install opendkim:
bash sudo apt install opendkim opendkim-tools
Generate DKIM keys:
bash sudo opendkim-genkey -s default -d example.com
Add the public key to your DNS.
Configure Exim to use DKIM:
bash sudo nano /etc/exim4/exim4.conf.template
Add or modify the DKIM-related settings.

DMARC: Publish a DMARC record in your DNS zone file.

   v=DMARC1; p=none; rua=mailto:dmarc-reports@example.com

Step 8: Monitor and Maintain

Regularly monitor Exim’s operation and logs to ensure everything is functioning smoothly. Keep the system and Exim updated with:

sudo apt update
sudo apt upgrade

Conclusion

With these steps, you should have a basic Exim installation and configuration running on your Debian system. Adjustments and advanced configurations can be made to tailor Exim to your specific needs. Always test configurations in a safe environment before applying them to production systems.