In this article, we will provide a comprehensive guide on how to set up DomainKeys Identified Mail (DKIM) for Ubuntu, Postfix, and Mailman. DKIM is an email authentication method that allows the receiver to check if the email was indeed sent by the domain it claims to be sent from and if the content was tampered with during transit.
Setting up DKIM for Ubuntu, Postfix, and Mailman involves installing OpenDKIM and OpenDKIM Tools, generating DKIM keys, configuring OpenDKIM and Postfix, creating Trusted Hosts, KeyTable, and SigningTable files, and restarting the services. It is a detailed process that requires following the steps carefully to ensure proper configuration and functionality.
Before starting, ensure you have the following:
- A server running Ubuntu.
- Postfix Mail Transfer Agent installed. If not, you can install it using
sudo apt-get install postfix.
- Root access or an account with
Step 1: Install OpenDKIM and OpenDKIM Tools
OpenDKIM is an open-source implementation of the DKIM sender authentication system. To install OpenDKIM and OpenDKIM Tools, run the following command:
sudo apt-get install opendkim opendkim-tools
Step 2: Generate DKIM Keys
Next, we need to generate a pair of DKIM keys (private and public) for your domain. First, decide on a selector, which is essentially a name that helps identify the DKIM public key in your domain’s DNS records. For instance, we’ll use ‘201205’ as our selector. Replace ‘example.com’ with your domain name and run:
sudo opendkim-genkey -s 201205 -d example.com
This command generates two files:
201205.txt (public key) and
201205.private (private key). The
-s parameter specifies the selector, and the
-d parameter specifies the domain.
Step 3: Configure OpenDKIM
Open the OpenDKIM configuration file with your preferred text editor. We’ll use
sudo nano /etc/opendkim.conf
Add the following lines to the configuration file:
Domain example.com KeyFile /etc/opendkim/201205.private Selector 201205 Canonicalization relaxed/simple Mode sv SubDomains yes Syslog yes UMask 022 UserID opendkim:opendkim KeyTable /etc/opendkim/KeyTable SigningTable /etc/opendkim/SigningTable ExternalIgnoreList /etc/opendkim/TrustedHosts InternalHosts /etc/opendkim/TrustedHosts Socket inet:8891@localhost
Domain specifies the domain for which emails will be signed,
KeyFile points to the location of the private key,
Selector is the selector we chose earlier,
Canonicalization specifies how messages should be prepared for signing,
Mode sets the operation mode,
SubDomains specifies whether to sign mail from subdomains,
Syslog enables logging to syslog,
UMask sets the UNIX file creation mask,
UserID specifies the user and group IDs for the filter,
KeyTable defines a file mapping key names to signing keys,
SigningTable maps addresses to key names,
InternalHosts specify files listing hosts that should be ignored or considered internal by the filter, and
Socket specifies the socket that will be used to communicate with Postfix.
Step 4: Configure Postfix
Open the Postfix main configuration file:
sudo nano /etc/postfix/main.cf
Add the following lines to the configuration file:
milter_default_action = accept milter_protocol = 2 smtpd_milters = inet:localhost:8891 non_smtpd_milters = inet:localhost:8891
milter_default_action specifies the default action when a milter application fails or times out,
milter_protocol defines the milter protocol version, and
non_smtpd_milters specify the milter applications for the SMTP server and non-SMTP server mail submission programs.
Step 5: Configure Trusted Hosts
Create the TrustedHosts file:
sudo nano /etc/opendkim/TrustedHosts
Add the domains, hostnames, and/or IP addresses that should be handled by OpenDKIM. Include localhost and your server’s IP address if applicable.
Step 6: Configure KeyTable and SigningTable
Create the KeyTable file:
sudo nano /etc/opendkim/KeyTable
Add the following line to the file, replacing “example.com” with your domain and “201205” with your chosen selector:
This line maps a key name to a signing key and its associated domain.
Next, create the SigningTable file:
sudo nano /etc/opendkim/SigningTable
Add the following line to the file, replacing “example.com” with your domain:
This line specifies which key to use for a particular address or domain.
Step 7: Restart the Services
Finally, restart the OpenDKIM and Postfix services for the changes to take effect:
sudo service opendkim restart sudo service postfix restart
Step 8: Test the DKIM Setup
To verify that DKIM is working correctly, send a signed email to a testing service or your own email account. Check the email headers to see if DKIM is included and properly configured.
Congratulations! You have successfully set up DKIM for Ubuntu, Postfix, and Mailman. This will greatly enhance the deliverability and trustworthiness of your emails. Remember to regularly check your DKIM setup to ensure it’s working as expected. Happy emailing!
DKIM stands for DomainKeys Identified Mail. It is an email authentication method that allows the receiver to check if the email was indeed sent by the domain it claims to be sent from and if the content was tampered with during transit.
DKIM is important because it helps verify the authenticity of emails and prevents email spoofing. It enhances the deliverability and trustworthiness of your emails, as recipients can verify that the email was sent by the claimed domain and has not been altered.
To set up DKIM for Ubuntu, Postfix, and Mailman, you will need a server running Ubuntu, Postfix Mail Transfer Agent installed, and root access or an account with sudo privileges.
To install OpenDKIM and OpenDKIM Tools, you can use the command
sudo apt-get install opendkim opendkim-tools.
To generate DKIM keys, you can use the command
sudo opendkim-genkey -s [selector] -d [domain]. Replace
[selector] with your chosen selector and
[domain] with your domain name.
To configure OpenDKIM, you need to edit the
/etc/opendkim.conf file. Add the necessary configuration lines, such as
To configure Postfix, you need to edit the
/etc/postfix/main.cf file. Add the lines
non_smtpd_milters to specify the milter applications and default actions.
To test the DKIM setup, you can send a signed email to a testing service or your own email account. Check the email headers to see if DKIM is included and properly configured.
It is recommended to regularly check your DKIM setup to ensure it is working as expected. This can help identify any issues or changes that may affect the deliverability of your emails.
While DKIM helps verify the authenticity of emails, it does not prevent all email-related issues. Other factors, such as SPF and DMARC, also play a role in email authentication and deliverability. It is recommended to implement a comprehensive email authentication strategy that includes DKIM, SPF, and DMARC for better protection against email-related problems.