The whole idea is based on the encryption and decryption of an additional signature, placed in the header of your message. To do this, you need to have two keys:
private key (which is unique to your domain and available only to you. Allows you to encrypt your signature in the header of your messages.)
public key (which you add to your DNS records using the DKIM standard, to allow your recipient's server to retrieve it and decrypt your hidden signature from your message header).
Take Game of Thrones to get the big picture of DKIM. Ned Stark sends a raven with a message to King Robert. Anyone could take a piece of paper, write a message and have Ned Stark sign it. But there is a way to confirm the message - a stamp. Now everyone knows that Ned's seal is direwolf (it's the public key). But only Ned has the original seal and can put it on his messages (it's the private key).
Setting up DKIM is just putting the public key information in your server records. It is also a txt record that needs to be put in the right place.
Once you set this up, every time someone receives an email from you, the recipient's server will attempt to decrypt your hidden signature using the public key. If successful, this will further authenticate your message and thereby increase the deliverability of all your emails.
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How to set up a DKIM record on your server step by step?
First you need to generate a public key. To do this, you need to log in to the admin console of your email service provider. The following steps may vary depending on your email provider.
If you use Google Apps to send email, here are the step-by-step instructions. Google Apps email users, you should know that DKIM signatures are turned off by default, so you need to manually turn them on in your Google Admin console.
Once you have the public key, you take the generated txt record and paste it into the right place in your DNS records.
Set up SPF and DKIM and improve your deliverability
If you send a lot of emails, whether it's for marketing or for inbound or outbound sales, your domain reputation is key and you should take very good care of it. You don't want your domain to be blacklisted and your email to end up in spam. Correctly setting up SPF and DKIM records on your DNS server is a necessary step towards the security of your domain and high deliverability of your messages.
Setup may seem complicated, but it's definitely worth the effort. If I were you, I'd go to my 8Core account and check that my SPF and DKIM are currently set up correctly, or ask my IT guys to do it (if you're not an 8Core user). And if the answer turned out to be "no", I would ask them to help me. And I wouldn't let them fool me. Not with this one.
Check the deliverability of your mail:
