DKIM (DomainKeys Identified Mail) — is a technology which combines few methods of antispam and antiphishing in order to increase the quality of classification and identification of legitimate emails. It confirms the identity of sender through a digital signature — the hidden code inside email content. So receiver will be sure, that the email is sent by you. To install DKIM for your domain, a TXT record with a public signature key must be created. It has to be set up on the server, that provides email sending.