Overview

DNS stands for (Domain Name System), and it's the backbone of online communication. We'll only cover the relevant basics here. You can find links to the official specifications in the resources section for more details.

A domain owner can publish something called a "TXT record" as a method of providing either instructions or information about their domain and activities relating to it. All of the DNS records Cordial uses are of this type.

What is a TXT record?

A TXT record is a specific type of DNS record stored in plain text, subject to certain formatting rules:

• All commas and exclamation points inside URLs in DNS records must be encoded (re-written) as %2C or %21, respectively.
• The string portion of a TXT record (the part in quotes) cannot be longer than 253 characters.
• All values in TXT records are case-sensitive, while the tag names themselves are usually case-sensitive. Therefore, as a best practice, Cordial recommends treating all elements of TXT records as case-sensitive.

Record types

TXT records all begin their string portion (the part in quotes) with v=. The value after the equals sign designates which kind of record it is. The values for the four types of records Cordial uses are spf1, DKIM1, DMARC1, and BIMI1.

• SPF (Sender Policy Framework): SPF allows a domain owner to specify who is authorized to send mail on their behalf.

• DKIM (Domain Keys Identified Mail): DKIM allows a server receiving a message to verify the original sender of that message using asymmetric key cryptography.

• DMARC (Domain-based Message Authentication, Reporting, and Conformance): DMARC allows a domain owner to further crack down on fraudulent messages by instructing the receiving server to take a specific action when a message fails to authenticate through either SPF or DKIM, including deleting the offending message before it ever reaches the customer.

• BIMI (Brand Indicators for Marketing Identification): BIMI allows a domain owner to have their logo displayed in a customer's inbox, next to the subject line.

Additional resources

• Official SPF Website
• RFC 7208: current official specifications for SPF. (RFCs are official specifications, so they're generally written in very dense technical language.)
• RFC 6376: current official specifications for DKIM.
• Official DMARC Website
• RFC 7489: current official specifications for DMARC.
• Official BIMI Website
• Most recent BIMI RFC draft (Link retrieved May 11th, 2022.)
• DNS article on Network Encyclopedia (Link retrieved May 19th, 2022.)
• RFC 1034 (Concepts) & RFC 1035 (Details): current official specifications for DNS.