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.
Prerequisites
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
sudoprivileges.
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-toolsStep 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.comThis 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 nano:
sudo nano /etc/opendkim.confAdd 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@localhostHere, 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, ExternalIgnoreList and 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.cfAdd the following lines to the configuration file:
milter_default_action = accept
milter_protocol = 2
smtpd_milters = inet:localhost:8891
non_smtpd_milters = inet:localhost:8891Here, milter_default_action specifies the default action when a milter application fails or times out, milter_protocol defines the milter protocol version, and smtpd_milters 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/TrustedHostsAdd 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/KeyTableAdd the following line to the file, replacing “example.com” with your domain and “201205” with your chosen selector:
201205._domainkey.example.com example.com:201205:/etc/opendkim/201205.privateThis line maps a key name to a signing key and its associated domain.
Next, create the SigningTable file:
sudo nano /etc/opendkim/SigningTableAdd the following line to the file, replacing “example.com” with your domain:
example.com 201205._domainkey.example.comThis 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 restartStep 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.
Conclusion
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 Domain, KeyFile, Selector, Canonicalization, Mode, SubDomains, Syslog, UMask, UserID, KeyTable, SigningTable, ExternalIgnoreList, InternalHosts, and Socket.
To configure Postfix, you need to edit the /etc/postfix/main.cf file. Add the lines milter_default_action, milter_protocol, smtpd_milters, and 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.
