Email Authentication in Microsoft 365

Why Email Authentication in Microsoft 365 is Important? – A Complete Explanation! 

On Day 23 of the Cyber security awareness month, learn why validating emails is important and how it strengthens Microsoft 365 email security. Stay tuned for more blogs in the M365 Cybersecurity blog series  

Recently, there’s been a troubling surge in email-related security threats within Microsoft 365. Ever wondered why email is such an easy target for breaches? Surprisingly, 25% of organizations lack essential email authentication mechanisms, and an alarming 10% only partially follow email auth standards. ⚠️

Clearly, these vulnerabilities have paved the way for a rise in email attacks within Microsoft 365. In response to this growing risk, Google has made an announcement, and they want all of us to prioritize email authentication measures seriously! Here’s a snippet from their recent announcement: 

Google announcement on new email authentication
Source: Google

Starting in 2024, Google will require strict email authentication for messages sent to Gmail accounts, and those sending over 5,000 emails per day to Gmail addresses will need to implement even more stringent authentication measures. 

Don’t be misled into thinking this is relevant for bulk email senders. Email authentication matters for everyone, regardless of the size of their email lists! It’s not just a Google-specific concern; Microsoft 365 admins should pay attention too! 💯 Because in the end, it doesn’t matter where your emails end up – whether it’s Google, Yahoo, Microsoft 365, or other email services. The ultimate goal is to validate emails thoroughly before they reach their intended recipients’ inboxes. ✅  

And if Microsoft 365 emails are not authenticated properly, a Non-Delivery Report (NDR) will be thrown like below: 


550-5.7.26 This mail is unauthenticated, which poses a security risk to the sender and Gmail users, and has been blocked. The sender must authenticate with at least one SPF or DKIM. For this message, DKIM checks did not pass and SPF check for [] did not pass with ip: [IPAddress]. 

So, never let that happen. Let’s see why validating and authenticating emails is crucial and outline the steps that Microsoft 365 sysadmins need to follow in the below parts. 

Why Email Verification is Important in Microsoft 365? 

Failing to implement proper email authentication in Microsoft 365 is a red alert that can expose your organization to various security risks. A few of them are:

  1. One of the most pressing dangers is the threat of phishing attacks, a critical concern for businesses.  
  1. Email spoofing is another concern where malicious actors manipulate email headers to make their messages appear genuine. 
  1. Domain impersonation is a very high-impact threat where attackers create domains resembling legitimate businesses to send seemingly trustworthy emails.  

But the spectrum of potential attacks doesn’t stop there! ❌The business email compromise (BEC) attack is a social engineering attack wherein attackers gain access to a legitimate email account and use it to send fraudulent emails that can result in significant financial losses. 

And the list of attacks doesn’t end here! 🔖Hence, the absence of robust authentication measures creates a significant vulnerability, making it easier for various attacks and phishing incidents. Therefore, proper email authentication in Microsoft 365 is not just a best practice but a critical step towards enhancing security. 

The ABCs of Email Authentication: SPF, DKIM and DMARC 

Now that we’ve got plenty of reasons to put our hands on doing email authentication. Then, it’s time to begin implementing robust email authentication types and ensure that our emails land only in legitimate mailboxes. These Domain Name Services (DNS) email authentication records verify that you are the legitimate sender of your email and prevent spoofing & phishing attacks.  

Primarily, Microsoft 365 uses SPF, DKIM, and DMARC authentication standards to verify every inbound email. Many organizations lack a clear understanding of email authentication, while attackers exploit this knowledge gap! That’s why here is a clear breakdown of how each email authentication works. 

Sender Policy Framework (SPF):

Sender Policy Framework (SPF) is a foundational email sender authentication mechanism used to verify that the sender’s server is authorized to send emails on behalf of a specific domain. 

How Microsoft 365 Uses SPF to Prevent Spoofing? 

Domain admins publish SPF TXT records in their DNS (Domain Name System) settings, listing the IP addresses or hostnames of servers that are allowed to send emails for their domain.  

A valid SPF TXT record contains the following elements: 

  • A declaration that this is an SPF TXT record (v=spf1). 
  • IP addresses that are allowed to send mail from the domain. 
  • External domains that can be sent on the domain’s behalf (for example, 

When an email is received, the recipient’s server checks the SPF TXT record to confirm whether the sending server is legitimate. Generally, if the sender’s server isn’t listed in the SPF record, the email is regarded as suspicious. 

DomainKeys Identified Mail (DKIM): 

So far, we’ve found a way to check whether it comes from a legitimate user or not. ✅Next, ensuring the integrity of your emails is paramount. That’s where DKIM (DomainKeys Identified Mail) comes into play, working tirelessly to protect your messages from unauthorized changes in transit! DKIM is a domain authentication mechanism that checks whether the email is received with the exact content that was sent. 

So, how does Microsoft 365 use DKIM to keep your email content intact and secure? Let’s see. 

How DKIM Prevents Email Message Tampering? 

The science behind DKIM: DKIM works by adding a digital signature to outbound emails. Then, the receiving email server can verify the signature using the sender’s public key. If the signature is valid, the receiving email server can be confident that the message has not been tampered with in transit. Overall, this allows senders to be sure that the message hasn’t been altered anywhere! 

Domain-based Message Authentication, Reporting and Conformance (DMARC) 

Email Authentication Basic Formula: SPF + DKIM = DMARC 

DMARC (Domain-based Message Authentication, Reporting, and Conformance) is a crucial email authentication framework. This enables domain administrators to set policies for handling emails that do not pass SPF and DKIM checks. 

How DMARC Reports Help to Validate Email? 

DMARC reports are sent to sender domain owners with a valid rua address in their DMARC records for further assessment. These reports cover: 

  1. The servers or services sending emails from your domain. 
  1. List servers/services that pass or fail DMARC authentication.  
  1. The actions taken by DMARC on servers receiving unauthenticated emails from your domain include None, Quarantine, or Reject. 

DMARC reports help identify legitimate senders and potential spammers, enhancing your domain’s email security. As a bonus, once a majority of emails pass DMARC, administrators can implement stricter DMARC policies, making it increasingly difficult for spoofers and phishers to operate. 

Benefits of Validating Emails in Microsoft 365: 

Now that we’ve seen what email authentication types to implement, right? Then, it’s high time to see what the advantages are we can benefit from successfully validating email.  

Enhanced Security: Email validation in Microsoft 365 helps to prevent phishing attacks, spam, and email spoofing. It ensures that incoming emails are from legitimate sources, reducing the risk of malicious emails reaching users’ inboxes.  

Improved Deliverability: Validating emails ensures that your legitimate messages are recognized as such by recipient email systems. This increases the likelihood of your emails being delivered to the intended recipients’ inboxes rather than being flagged as spam.  

Reduced Phishing Risk: By validating emails, you can decrease the likelihood of phishing emails reaching your users’ inboxes. This helps protect sensitive data, user credentials, and financial information from falling into the wrong hands.  

Brand Reputation: Email validation safeguards your brand’s reputation by preventing cyber criminals from tarnishing it through phishing attacks. Protecting your reputation is crucial for maintaining customer trust and loyalty.  

Efficient Email Management: Validating emails helps reduce the number of unwanted or malicious emails in your organization’s inboxes. This saves time and resources by minimizing the need to deal with spam and phishing attempts. 

Closing Thoughts: 

In a world where email communication is more critical than ever, email authentication is the linchpin of your organization’s security and reputation. Therefore, by using SPF, DKIM, DMARC, and their reporting capabilities, you can shield your organization from phishing and spoofing attacks. Additionally, make sure to implement a robust Microsoft email security system to ensure a safe work environment for your users, seamlessly integrated into your workflow. ✅ 

While Google’s upcoming rules shed light on the importance of email authentication, Microsoft 365 administrators must recognize that email authentication is not just a security measure—it’s a strategy to enhance their organization’s email communication and digital presence. 

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Why Email Authentication in Microsoft 365 is Important? – A Complete Explanation! 

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