How to fix compauth failure in email headers due to domain alignment issues?
Matthew Whittaker
Co-founder & CTO, Suped
Published 22 Jun 2025
Updated 19 Aug 2025
9 min read
Email headers can sometimes present puzzling authentication failures, and one that often catches senders off guard is compauth=fail reason=001. This specific error indicates an issue with Composite Authentication, a system primarily used by Microsoft to verify email authenticity. It's a signal that your email hasn't passed all necessary checks, often due to a mismatch in domain alignment.
Domain alignment is critical for modern email authentication protocols like DMARC. It ensures that the domain visible to the recipient (the 'From' address) is consistent with the domains used for SPF (Sender Policy Framework) and DKIM (DomainKeys Identified Mail) authentication. When these domains don't align, receiving servers, especially those utilizing Composite Authentication, can flag the email as suspicious, leading to deliverability issues.
If your emails are hitting spam folders or getting rejected because of compauth=fail, you're not alone. Many senders face this, particularly when using third-party email service providers (ESPs). Understanding how to correctly configure your SPF, DKIM, and DMARC records for proper domain alignment is key to resolving these frustrating delivery failures and improving your overall email deliverability. This guide will walk you through the steps to diagnose and fix these problems.
Let's dive into the specifics of Composite Authentication, domain alignment, and how to get your emails successfully delivered.
Composite Authentication (Compauth) is Microsoft's proprietary authentication check, a robust system designed to protect users from phishing and spam. Unlike standard SPF and DKIM checks, which primarily verify the sender's infrastructure, compauth takes a broader view. It aggregates the results of various authentication methods like SPF, DKIM, and DMARC, and then evaluates the overall trustworthiness of the email based on domain alignment and other factors.
When you see compauth=fail reason=001 in your email headers, it specifically points to a failure in this composite check. The most common cause is a domain alignment issue. This means that while your SPF or DKIM might technically 'pass' individually, the domains associated with these checks don't align with the domain in the 'From' header, which is the address recipients actually see.
DMARC (Domain-based Message Authentication, Reporting, and Conformance) is the protocol that mandates this alignment. It has two primary alignment checks: SPF alignment and DKIM alignment. For an email to pass DMARC and subsequently compauth (especially for Microsoft recipients), at least one of these alignment checks must succeed.
Alignment Type
Description
SPF alignment
The domain in the 'Return-Path' (or MAIL FROM) header must match or be a subdomain of the domain in the 'From' header. This is often an issue with third-party senders that use their own domains in the Return-Path.
DKIM alignment
The domain in the DKIM signature's 'd=' tag must match or be a subdomain of the domain in the 'From' header. If your emails aren't signed with your domain, this will fail.
A failure in either SPF or DKIM alignment, even if the base authentication (SPF pass, DKIM valid signature) is technically present, will cause DMARC to fail for that specific method. If both fail, then DMARC fails, which in turn leads to a compauth=fail result.
Diagnosing the alignment issue
The first step in resolving any email authentication problem is to examine the email headers. These headers contain a wealth of information about how an email was processed by various mail servers, including the results of SPF, DKIM, and DMARC checks, and critically, the Authentication-Results header. This specific header will show you exactly why compauth=fail occurred.
Example of an authentication-results header
Authentication-Results: spf=pass (sender IP is 200.58.101.8)
smtp.mailfrom=mail01.ferozo.com; live.com.ar; dkim=none (message not signed)
header.d=none;live.com.ar; dmarc=none action=none
header.from=doroteadesign.com.ar;compauth=fail reason=001
In the example header, notice the spf=pass and dkim=none (message not signed). Crucially, the header.from domain is doroteadesign.com.ar, while the smtp.mailfrom domain (used for SPF) is mail01.ferozo.com. This is a clear SPF alignment failure. Additionally, with dkim=none, DKIM alignment is also not possible. These misalignments directly contribute to the compauth=fail.
Common culprits behind these domain alignment issues include using email service providers that do not offer custom return-path domains, or not enabling DKIM signing for your custom domain. In scenarios where you lack direct access to DNS for certain sending domains, you will need to engage your provider to implement the necessary changes. Reviewing the email headers is the first step to pinpointing the exact cause. You can also refer to our guide on why SPF passes but Google Postmaster Tools does not for more insights.
Fixing SPF and DKIM alignment
To fix SPF alignment issues, the domain in the Return-Path header (also known as MAIL FROM) needs to match your 'From' header domain (or be a subdomain of it). Many third-party email services send emails using their own domain in the Return-Path. To correct this, you generally need to set up a custom return path or custom MAIL FROM domain within your ESP's settings. This often involves adding a CNAME record to your DNS that points to your ESP's servers.
For DKIM alignment, the domain specified in the 'd=' tag of the DKIM signature must align with your 'From' header domain. If your emails show 'dkim=none' or a different domain in the 'd=' tag, you need to configure DKIM for your sending domain. This typically involves generating a DKIM public key from your ESP and adding it as a TXT record to your domain's DNS. Ensuring that your emails are properly DKIM-signed with your domain is a strong signal of legitimacy.
Key actions to take
Custom Mail FROM: Configure your ESP to use a custom Mail FROM (Return-Path) domain that aligns with your From header. This is often a subdomain you set up.
Enable DKIM: Ensure DKIM signing is active for your main sending domain (not just your ESP's default). You may need to add a DKIM TXT record to your DNS. We have a guide on how to fix DKIM from domain mismatch.
Check alignment mode:DMARC allows strict or relaxed alignment. Relaxed mode is often sufficient to pass alignment, especially when using subdomains. Strict mode requires an exact match.
Engaging with your email provider or hosting service is crucial if you do not have direct access to your domain's DNS records. They should be able to assist in configuring custom Mail FROM domains and enabling DKIM signing for your domain.
Implementing DMARC for enforcement
While SPF and DKIM are the foundational authentication methods, DMARC is the policy layer that ties them together and dictates how receiving servers should handle emails that fail authentication or alignment. If your emails are failing compauth, it often means your DMARC policy is either not implemented, or not robust enough to enforce authentication correctly. Establishing a DMARC record is a critical step in addressing compauth=fail.
A DMARC record, published as a TXT record in your DNS, allows you to tell receiving mail servers what to do with emails that fail DMARC authentication (i.e., SPF or DKIM alignment fails). The policy (p= tag) can be set to none, quarantine, or reject. Starting with p=none is advisable to gather DMARC reports and understand your email flow before enforcing stricter policies.
Once you have addressed your SPF and DKIM alignment issues, you can gradually move your DMARC policy to p=quarantine or p=reject. This will tell receiving mail servers, including those using Composite Authentication, to treat non-aligned emails more strictly. Remember, DMARC reports are invaluable for monitoring your email authentication performance and identifying any new alignment issues. You can find more details in our guide on how to safely transition your DMARC policy.
Maintain a healthy sending reputation
Beyond the technical fixes, it's essential to maintain a healthy sending reputation to ensure your emails reliably reach the inbox. Even with perfect authentication, poor sending practices can lead to emails being flagged as spam or blocklisted (blacklisted).
Positive reputation impact
When your SPF, DKIM, and DMARC are correctly aligned, it builds trust with receiving mail servers. This significantly boosts your domain's reputation and improves inbox placement. Mailbox providers, including Outlook and Gmail, prioritize authenticated email.
Improved trust signals: Proper alignment is a key indicator of legitimate sending practices.
Reduced spam flagging: Authenticated emails are less likely to be marked as spam.
Regular monitoring of your DMARC reports is essential. These reports provide invaluable feedback on your email authentication status, showing you which emails are passing or failing DMARC, and why. They can help you spot new alignment issues or unauthorized sending activity using your domain. Monitoring helps you maintain strong email security and deliverability.
In addition to technical setup, consistently sending valuable and relevant content to engaged subscribers will positively impact your sender reputation. A high unsubscribe rate or spam complaint rate can quickly degrade your reputation, regardless of your authentication setup, leading to more emails landing in the junk folder or on a blocklist.
Views from the trenches
Best practices
Always enable DKIM for your primary sending domain to ensure message integrity and alignment.
Work with your email service provider to implement a custom Mail FROM domain.
Start with a DMARC policy of p=none and analyze reports before moving to stricter policies.
Common pitfalls
Not having DKIM enabled for your 'From' domain leads to instant DMARC alignment failures.
Using a generic Mail FROM domain from an ESP, which breaks SPF alignment.
Setting a DMARC policy to p=reject too early, causing legitimate emails to bounce.
Expert tips
Implement a DMARC reporting tool to gain clear visibility into your email authentication status.
For complex setups, consider consulting with an email deliverability specialist to fine-tune configurations.
Educate your team on the importance of email authentication and its impact on deliverability.
Expert view
Expert from Email Geeks says that Microsoft's `compauth=fail` with reason `001` signals their new authentication solution is failing because domains are not properly aligned.
2020-03-06 - Email Geeks
Expert view
Expert from Email Geeks says that to fix `compauth=fail`, you should add DKIM and DMARC records specifically for your primary sending domain, for instance, `doroteadesign.com.ar`.
2020-03-06 - Email Geeks
Key takeaways for reliable email delivery
Resolving `compauth=fail` in email headers, particularly when it stems from domain alignment issues, is crucial for successful email delivery. This involves a clear understanding of how SPF, DKIM, and DMARC work together and how their associated domains must align with your 'From' header domain.
By correctly configuring your custom Mail FROM domain and ensuring your emails are DKIM-signed with your branding, you can overcome these authentication hurdles. Implementing DMARC with a proper policy further solidifies your domain's authenticity and helps receiving servers, including Microsoft's Composite Authentication, trust your emails. Consistent monitoring through DMARC reports will allow you to quickly identify and address any future issues, maintaining optimal email deliverability.
Prioritize these authentication best practices to ensure your messages always reach their intended recipients, free from authentication failures.
Microsoft to verify email authenticity. It's a signal that your email hasn't passed all necessary checks, often due to a mismatch in domain alignment.
Microsoft's proprietary authentication check, a robust system designed to protect users from phishing and spam. Unlike standard SPF and DKIM checks, which primarily verify the sender's infrastructure, compauth takes a broader view. It aggregates the results of various authentication methods like SPF, DKIM, and DMARC, and then evaluates the overall trustworthiness of the email based on domain alignment and other factors.
Outlook and 
Gmail, prioritize authenticated email.
