---
title: "Basics of DKIM syntax and tags | DuoCircle"
description: "Learn how a DKIM record is structured: the syntax, the required and optional tags like v=, a=, d=, and s=, and what each one means for email authentication."
image: "https://www.duocircle.com/images/og-default.png"
canonical: "https://www.duocircle.com/blog/email-security/basics-of-dkim-syntax-and-tags/"
---

Quick Answer

A DKIM record is a DNS TXT record with tag=value pairs. Core tags: v= (DKIM1), a= (algorithm, typically rsa-sha256), b= (signature), bh= (body hash), c= (canonicalization), d= (signing domain), h= (signed header fields), s= (selector), and p= (public key). Receivers fetch it at selector.\_domainkey.yourdomain.com to verify the message.

Basics of DKIM syntax and tags

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![DKIM syntax and tags](https://media.mailhop.org/duocircle/images/2024/12/spf-record-tester-4.jpg) 

DKIM stands for DomainKeys Identified Mail, a cryptography-based [email authentication](/resources/email-authentication) protocol that helps receiving servers verify if an email sent from your domain was tampered with in transit. If you have DKIM deployed for your domain, then your server will affix a digital signature to the header with each outgoing email. This is a **cryptographically secured signature** that is produced using a private key that is known only to you. The counterpart of the private key is a public key, which is published in the DNS of your domain.

When the receiving server processes your email, it fetches the [public key](https://en.wikipedia.org/wiki/Public-key%5Fcryptography) to confirm its authenticity and **verify the message** remained unaltered during transit.

## Why is DKIM helpful to domain owners?

DKIM helps **domain owners** in their efforts to prevent their domain from getting involved in [phishing and spoofing attacks](https://thehackernews.com/2024/07/proofpoint-email-routing-flaw-exploited.html). It basically verifies the legitimacy of outgoing emails. This keeps their brands out of financial and legal problems.

What else [DKIM](/resources/what-is-dkim) does is improve the [sender’s reputation](https://sendpulse.com/support/glossary/sender-reputation), which means mailboxes regard your **domain as genuine and trusted**. If this happens, most of the emails sent by you will land in the desired recipients’ inboxes instead of [spam folders](https://cybernews.com/news/microsofts-breach-notification-emails-end-up-in-spam-folder/). _Deploying DKIM is also mandatory compliance with many regulations, so if your brand falls under any of such compliances, you will need DKIM_.

[![spam folders](https://media.mailhop.org/duocircle/images/2024/12/spf-permerror-3.jpg)](https://media.mailhop.org/duocircle/images/2024/12/spf-permerror-3.jpg)

## DKIM syntax

DKIM publishes the public key and associated information using a [DNS TXT record](https://www.cloudflare.com/learning/dns/dns-records/dns-txt-record/). The record’s syntax comprises various tags, each serving a specific purpose. Below are the most common tags found in DKIM records:

- **v**: Denotes the **DKIM version**. Currently, the only version available is v=DKIM1.
- **a**: Indicates the algorithm used to generate the DKIM signature. Common values include rsa-sha256 and rsa-sha1.
- **b**: Represents the actual digital signature of the [email headers](https://proton.me/blog/what-are-email-headers) and body, encoded as a base64 string and generated using the [private key](https://www.investopedia.com/terms/p/private-key.asp).
- **bh**: Stands for “body hash,” which is the hash of the canonicalized email body, encoded as a base64 value.
- **c**: Specifies the canonicalization algorithms applied to the header and body. Common options are simple/simple, relaxed/simple, and relaxed/relaxed.

[![outgoing emails](https://www.duocircle.com/wp-content/uploads/2024/12/spf-validator-2.jpg)](/wp-content/uploads/2024/12/spf-validator-2.jpg)

- **d**: Refers to the domain name of the signing entity. If you’re creating the [DKIM record](/resources/dkim-checker), include your domain name here. Ensure the domain matches or is a subdomain of the one used in the ‘From’ header of your outgoing emails.
- **h**: Lists the signed header fields, separated by colons. For example, h=from:to:subject:date.
- **i**: _An optional identity representing the user or agent on whose behalf the email is signed. For instance, i=[user@eng.example.com](mailto:user@eng.example.com)_.
- **l**: Known as the body length count tag, it indicates the **number of body bytes** included in the hash.

[![dkim record statistics](https://media.mailhop.org/duocircle/images/2024/12/DKIM-Record-Statistics.jpg)](https://media.mailhop.org/duocircle/images/2024/12/DKIM-Record-Statistics.jpg)

## Final words

These DKIM tags convey essential information that enables the **receiving server** to verify the authenticity of emails sent from your domain. _Therefore, it’s crucial to create your DKIM record with care_. If you need assistance with email authentication, feel free to [contact us](/contact) or book a demo with [DuoCircle](/) for expert support.

## Topics

DKIMemail headerTags 

![Brad Slavin](https://media.mailhop.org/dmarcreport/images/team/brad-slavin.jpg) 

Brad Slavin 

General Manager

General Manager at DuoCircle. Product strategy and commercial lead across the email security portfolio.

## Secure your email infrastructure

Protect, authenticate, and deliver. Contact our team to find the right solution.

[Contact Sales](/contact/) [Explore Products](/products/) 

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