SPF, DKIM and DMARC are three technical records in the domain's settings that prove to the receiving server that a message is from you. SPF determines which servers are allowed to send mail on your behalf. DKIM adds a cryptographic signature to every message, which verifies that the content was not altered along the way and that it originates from your domain. DMARC tells the recipient what to do if verification fails – do nothing, place it in spam, or reject the message – and at the same time sends you reports on who is sending mail in your name. Without these records, deliverability falls, and anyone can send fraudulent messages with your address as the sender. Setting them up is the domain administrator's job, and they need to be added for every new tool that sends mail on your behalf.
See also: Email Deliverability, Domain warming, Access policy for company accounts.
