What is Email Authentication? A Look at The Most Common Methods

Robert BrandlCai Ellis

By Robert & Cai

See Updates
Email Authentication

Email authentication is a process of verifying the identity of an email sender. This helps to ensure that the email is coming from a trusted source, and not from a spammer or phisher.

This will help improve your email deliverability, as the likelihood of your emails and newsletter going to spam increases if you aren't using any authentication methods.

There are several methods of email authentication, which we are going to discuss now.

Why is email authentication even a thing?

The main issue with email is that it's an open protocol that allows spammers to use email addresses they don't own. You may wonder how they do that.

Or how I once managed to send an email with the sender address Only as a test to myself, of course.

email spoofing examples

Because if you sign up for an account with a legitimate email marketing service, one of the first things they ask you to do is confirm your email address.

This way Mailchimp, GetResponse, etc. will know that you are a legitimate sender (well, maybe not in every case but at least you are able to access emails under your company's domain name). Sometimes they will also ask you to confirm domain ownership by adding a record to your domain's DNS.

DNS stands for Domain Name System. It is a system that converts human-readable domain names (e.g. into computer-readable IP addresses. Without it, web browsing and sending email would be very difficult. DNS servers are like the phone books of the Internet, they keep a directory of domain names and translate them to IP addresses when requested.

Every owner of a domain name has access to their domain's DNS via the domain registrar's account (e.g. Namecheap, GoDaddy). Once you are logged in, you will be able to edit your DNS records. Common DNS records include A records, which map a domain name to an IP address, and MX records, which map a domain name to an email server.

But there are other ways than using legitimate ESPs to send emails – dark places where they won't ask you to confirm your email address as long as you flash the cash (or Bitcoin).

Unfortunately, it's still good business to send out phishing scams and other malicious emails. To stop this from happening, the following four authentication methods got created.

The most important authentication methods

These are the most common methods:

  1. SPF (Sender Policy Framework)
  2. DKIM (DomainKeys Identified Mail)
  3. DMARC (Domain-based Message Authentication, Reporting & Conformance)
  4. BIMI (Brand Indicators for Message Identification)

Let's take a closer look at each of them.

1. Sender Policy Framework (SPF)

The most basic form of email authentication is Sender Policy Framework (SPF). SPF allows you to specify which email servers are allowed to send emails on behalf of your domain.

spf authentication

How SPF Authentication works – by EmailOnAcid

To set up SPF authentication, you will need to add a TXT record to your DNS settings. This TXT record contains a list of server names or IP addresses that are authorized to send emails for your domain.

If an email comes from a mail server that is not on this list, it will fail the SPF check and is more likely to be stopped by the spam filters. For that reason, it's very important to add all the different services you are using. In our case, we are sending emails via Google Workspace and Mailchimp (which uses, for example.

Here is a sample SPF record:

"v=spf1 mx a ~all"

For example, this record allows the mail server to send email on our behalf. We are using this SPF record because we are Google Workspace customers. By setting it up for our domain name, we tell mailbox providers like Outlook and AOL that it's fine for Google servers to handle email for our Tooltester email addresses.

And because we are also sending emails via Mailchimp, we have another “include” record, indicating that is also allowed to send on our behalf.

SPF authentication is not the most secure way to prevent your domain from being spoofed because anyone can look into your SPF records, and try to use the allowed servers (Google in our case). In this particular case, though, Google would not allow anyone else to set up the domain name in their Google Workspace account.

2. DomainKeys Identified Mail (DKIM)

This is a more advanced form of email authentication that uses cryptographic signatures to verify the authenticity of an email.

dkim authentication

How DKIM works – by EmailOnAcid

When you set up a DKIM signature, you will need to generate a public and private key pair. The private key is used to sign each outgoing email, and the public key is published in your DNS records.

When an email arrives at its destination, the receiving server can use the public key to verify that the signature on the email matches the private key and that the email has not been tampered with.

If the signature does not match, or if the message has indeed been tampered with, DKIM will fail and the email is more likely to be marked as spam.

Here is a sample DKIM record from MailerLite, which we use to send out the results of our deliverability tests:

k=rsa; p=MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQDhXpjoxP3ANucOq4awUl53QXp7QSrbI2xOzSTigQ68XUi6kKifXkhL/a0GkSQ9HQm+PmvlkIC4wAyI9Cf6RW8bim80jSAeQJbGYAPyTAbxxTqu+h2deO8ffLfX2jRqAs73Jpgn3XyQSCIClUyTJQR9e0/BIwvnHQlSKJA1PcgwIDAQAB

Adding this record to our DNS will allow MailerLite to send emails on our behalf. Basically, DKIM authentication is very similar to SPF but more secure due to the fact that there is a private key involved.

3. Domain-based Message Authentication, Reporting & Conformance (DMARC)

This is the most advanced and secure form of email authentication. DMARC builds on SPF and DKIM, and adds a few more features.

With DMARC, you can specify what to do if an email fails either the SPF or DKIM checks. You can choose to have the email rejected or delivered to the spam folder. There is also a “none” policy which just means that the email will be delivered normally, but the DMARC record will still collect data about failed authentication attempts.

DMARC policy

DMARC authentication process – by EmailOnAcid

DMARC also allows you to set up email forwarding so that you can get reports about failed authentication attempts. These reports can be very helpful in troubleshooting why your emails are not being delivered.

Here is a sample DMARC record:

v=DMARC1; p=quarantine;

This DMARC record is set to the “quarantine” policy, which means that emails that fail the SPF or DKIM checks will be delivered to the spam folder. The “rua” tag specifies where to send DMARC reports.

A concrete example:

If a spammer is trying to send emails using a email address, they will fail SPF and DKIM. The DMARC record indicates that such emails should go to the spam folder of the recipient.

Brand Indicators for Message Identification (BIMI)

This is a new standard that is not yet widely adopted, but it shows promise. BIMI allows you to insert your brand logo into the headers of your emails so that recipients can see at a glance that the email is from you.

It partly security, partly marketing. The idea is that if people see your logo in their email client, they will be more likely to trust the email and less likely to mark it as spam.

To set up BIMI, you need to generate a validator certificate and publish it in your DNS records. You also need to have a verified sending domain and a published DMARC record.

Example of a BIMI record: IN TXT "v=BIMI1; l=;"

This record specifies the location of the brand logo that will be used for BIMI.

Once BIMI is set up, your logo will appear next to your email in the recipient's inbox:

deliverability newsletter

How to quickly check whether an email passes SPF, DKIM and DMARC

The easiest way to check whether an email passes SPF is to open the email in Gmail, click the three dots and then select “Show original”. You'll then see an analysis for SPF, DKIM and DMARC as part of the email header:

gmail email header

How to Set Up Email Authentication

Setting up any of the email authentication methods requires you having access to your domain's DNS records. Any owner of a domain name has access through their domain registrar's web interface (e.g. Namecheap, GoDaddy, etc.).

The basic setup process is straightforward:

1) Once you have the authentication record (SPF, DKIM, etc.) from your email service provider, you access the backend of your web hosting provider.

See Namecheap's example here. It's under Advanced DNS:

namecheap advanced DNS

Then you go ahead and add a new record. In this case, it's a TXT Record for our SPF signature:

namecheap DNS

If you are unsure what to do, it's always best to ask support. Most web hosting companies offer live chat support and are very helpful from my experience.

How do I know if the authentication was successful?

If you are using an email marketing service such as Mailerlite, they will check it for you as you can see in the screenshot:

domain authentication

Additional Tips to get your emails delivered

Monitor your email deliverability

Use tools like Glockapps or Mailtester to monitor your email deliverability. These will give you a detailed report and show you whether your emails are getting delivered, bounced or marked as spam. See this sample report from Glockapps:

glockapps results

Glockapps will also show you whether your emails are passing SPF, DKIM and DMARC. This is very helpful for troubleshooting why some of your emails are not being delivered.

Use a consistent sender address

When sending emails, don't swap around your sending domain or email addresses. Use the same email address, so the mailbox provider will learn that your recipients like to receive email from that email address. Also, you can ask your recipients to add your sender email address to their contacts.

Send relevant and targeted content

Needless to say, the more relevant and targeted your email's content is, the less likely it is to get flagged as spam (ideally it's the opposite: people will flag you as a safe message should you ever get caught by a spam filter). Use double opt-in to make sure that people who sign up actually want to hear from you.

Start a conversation

Are you also sometimes annoyed by email addresses?

I get that it can be annoying if people start responding to your newsletter just by hitting the “reply” button. The good thing, though, is that email providers (Gmail, Outlook, etc.) see this as a positive indication that people actually want to receive your emails.

Practice list hygiene

Email lists that are not well-maintained are more likely to get flagged as spam or not delivered at all. This means you need an email list management strategy that includes regularly removing bounced emails, unsubscribes and people who never engage with your emails.

There are also plenty of email cleaning services (e.g. BriteVerify, QuickEmailVerification, MailerCheck) that can help you with this.

And lastly, don't forget the basics

Avoid using spammy words in your email subject lines, don't buy email lists and don't send emails too often. If you need more contacts, check out our complete guide to how to build an email list.

If you’d prefer to learn by watching, follow our Email Deliverability Best Practices video:

Email Deliverability Best Practices

Wrapping Up on Email Authentication

Email authentication does not guarantee that your email marketing strategy will be a success, but it's an important part of the puzzle. In combination with other email deliverability best practices, you can make sure that your emails have a much higher chance of reaching the inbox.

It's also a good idea to go the next step and set up BIMI as well, as it can help improve your deliverability by showing recipients a branded logo in the inbox.

Not setting this up properly from the start would be a big mistake, so make sure you prioritize email authentication.

Do you have any questions about email authentication or deliverability in general? Let me know in the comments!

email marketing ebook

Email Marketing Crash Course: Step-by-Step Guide

Our email marketing course for beginners: ideal for small and medium-sized businesses, online stores and bloggers. It shows you all the steps you need to send your first email campaign. Best of all, it’s free!

Sign up to receive your copy immediately!

Your subscription could not be saved. Please try again.
Your subscription has been successful.

The authors

Learn more about us

Robert Brandl

Founder and CEO

Hello! I'm Robert, an email marketing expert with over 15 years of experience in the industry. After honing my skills by serving major corporations working for an agency, I founded EmailTooltester as a passion project to help small and medium-sized businesses. My goal is to assist you in maximizing email marketing's potential.

Cai Ellis

SEO Manager

Hi! My name is Cai, and I've worked in digital marketing for many years. More recently, I've been concentrating on email marketing, through testing tools and writing guides. And I've also picked up a bit of SEO know-how along the way! If you've got questions about these or any related subjects, I'll be happy to help!

Learn more about us

We keep our content up to date

22 Aug 2023 - YouTube Video Added
02 June 2023 - Illustrations added

Our Methodology

This article has been written and researched following our EmailTooltester methodology.

Our Methodology