Using DKIM For Your Emails

Domain Keys Identified Mail lets domains take responsibility for the emails they send out by confirming they are the true senders. It was introduced as a way to combat email spoofing, where the email address is forged so the message appears to have come from someone or somewhere other than the actual source. Many unscrupulous people use forged email addresses to send spam or online scams.
Email service providers have caught on to this. To protect their users, many service providers are automatically filtering out any emails without DKIM - whose domains are not verified. These emails would either get blocked completely or re-routed to the spam folder.
As of version 4.70, Exim (the email server) has native support for DKIM, which means that it would automatically locate the DKIM key and sign all out-going email messages. This makes setting up DKIM much easier, especially for people with limited knowledge of server administration. If you have the latest version of cPanel, simply log into your domain's cpanel account and go to the 'Email Authentication' and enable DKIM. Once enabled the system will generate the key and display it on the page.
Next, you will need to add the DKIM key to your DNS record. You can do this on cPanel. If your domain is managed by the domain registrar such as Godaddy, you will be able to update the DNS record via your online account. Simply go to the DNS manager and create a new txt record. Copy and paste the key generated by the system into the txt file, save and you are good to go. The DNS records may take a few hours to fully update so just be patient.
You can do a few tests to see if the outgoing emails are being signed with DKIM. Simply send a few emails to yourself from any email address of your domain. Once you have received the emails in your inbox, open them and view message source. If it says 'DKIM = pass' it means everything is working properly. Please note DKIM verification will fail in Hotmail if the message body is empty.
How does DKIM work
When the email service provider receives an email, it looks up the DNS record of the sender domain and locates the DKIM key. It then looks for the DKIM signature in the email message. If there is a match, the DKIM verification is passed and the email gets delivered. Otherwise the verification fails and the system will block the email or re-route it to the spam folder.