Why Email Aliases Fail DMARC (And How to Fix Them)
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An email alias is an alternative email address that redirects messages to a primary email inbox. An alias does not have its own mailbox and is simply responsible for forwarding messages to one or more designated email addresses.
DMARC can fail for email aliases depending on how the message is altered during forwarding. In this blog, we will break down the various scenarios affecting DMARC authentication for email aliases.
Key Takeaways
- Email aliases often break DMARC due to SPF and DKIM domain misalignment during forwarding.
- SPF fails because the forwarding server isn’t authorized in the original sender’s SPF record.
- DKIM may survive, but can fail if message content is altered (e.g., added footers).
- ARC preserves original authentication results, helping legitimate forwarded emails pass DMARC.
- To ensure a smooth setup, start with DMARC p=none, monitor reports, and gradually enforce stricter policies.
- PowerDMARC helps evade DMARC failures by providing hands-on, rapid human support and managed services.
Reasons for DMARC Failure for Email Aliases
DMARC may fail for email aliases, depending on how the alias is configured and how the forwarding process alters the original message. Whether you send personalized emails that are perfectly legitimate, the following scenarios can affect authentication:
1. Forwarding Can Break SPF
SPF verifies whether a sending IP is authorized to send emails on behalf of a domain. When an email alias forwards an email, the forwarding server then becomes the “sender” who may not be listed in the sending domain’s SPF record. This causes SPF to fail.
For example:
- From: [email protected]
- Return-Path: [email protected]
- Since the “From” domain and the Return-Path domain don’t align, SPF fails.
DMARC checks that the domain in the visible “From” address matches the domains used for authentication (SPF or DKIM). In this case, if your DMARC policy relies solely on SPF authentication, DMARC will fail too.
2. DKIM May Survive, But Not Always
DKIM may survive forwarding scenarios as authentication depends on message content. When an alias forwards an email, message content often remains intact, with changes to the header. However, this is not always the case. Some forwarders also alter message content and insert additional footers, which may cause DKIM to fail.
In such cases, even if your DMARC policy relies on DKIM as well, DMARC will inevitably fail for the message.
How to Diagnose DMARC Alias Failures
Here are two easy steps to follow to diagnose DMARC alias failures.
Manual Method: Check DMARC Reports for Alignment Failures
Go through your DMARC aggregate or failure reports for messages sent from alias domains.
Look for alignment failures in DMARC aggregate reports under the <policy_evaluated> section, where you’ll see <spf>fail</spf> or <dkim>fail</dkim>.
Example failure report:
“reason”: “spf fail”,
“header_from”: “[email protected]”,
“disposition”: “reject”
This means the email from your alias did not pass SPF alignment. It has triggered your DMARC policy and caused rejection.
Automated Method: Using a DMARC Report Analyzer
You can use PowerDMARC’s DMARC Report Analyzer tool to convert complex DMARC XML reports into easy-to-understand charts and graphs. It helps you:
- Continuously monitor your email traffic
- Track deliverability issues and authentication failures
- Interpret authentication data easily and effectively
- Schedule on-demand PDF reports that can be exported in PDF or CSV format
Fixes for DMARC Alias Problems
Before you make any of the below fixes, always review these changes with your technical team.
1. SPF Alignment for Aliases
Add the sending IPs or include mechanisms of the forwarding or third-party service to the SPF record of the alias domain.
Example:
v=spf1 include:_spf.google.com include:helpscout.com ~all
This ensures the forwarding servers are authorized in SPF, similar to whitelisting trusted senders. This will ensure the bouncer (SPF) lets them in without any conflict or trouble.
2. DKIM Signing for Alias Domain
Configure your mail system or provider to sign outgoing emails with DKIM using the alias domain, not just the forwarding address.
It’s like stamping your family crest (DKIM signature) on every letter you send from your house (alias domain). In this way, everyone will know exactly where it came from — even if someone else delivers it.
3. Enable ARC for Your Domain
Authenticated Received Chain (ARC) preserves a message’s original authentication results (SPF, DKIM, and DMARC) as the email passes through intermediary servers. Finally, it allows the final receiving server (e.g., Gmail, Outlook) to trust the original authentication, even if it gets broken along the way. However, it’s important to note that not all email providers honor ARC (e.g., some may still reject forwarded emails).
4. Subdomain Strategy
Instead of using aliases, create dedicated subdomains for different purposes (e.g., [email protected]).
To better understand this, think of building separate mailboxes for each family member (subdomains) instead of sharing one. This way, everyone gets their own keys and address, making it much easier to manage and secure the mail.
DMARC Policy Recommendations for Aliases
Follow the below DMARC recommendations that are applicable for aliases, but for other use cases as well.
Start with p=none
Start with p=none to monitor DMARC activity without impacting email delivery. This helps identify alias-related alignment issues without risking email delivery. It’s like installing security cameras before locking the doors. It enables you to first watch what’s happening, so you know exactly where the problems are.
Gradual enforcement
Only move to p=quarantine after resolving SPF/DKIM alignment problems for your aliases. This filters suspicious emails while minimizing impact on legitimate messages. Think of it as putting suspicious mail in a holding area (quarantine) instead of throwing it out, until you’re sure it’s safe.
Move to p=reject with caution
Use p=reject only when you know all aliases are fully authenticated and aligned. Strict rejection can block legitimate emails if aliases aren’t properly configured. Using reject prematurely can block legitimate messages, leading to email deliverability issues.
Pro Tips to Prevent Future Issues
Here are some pro tips to avoid alias-related issues in the future.
Use DMARC Analyzers
Always track alias-specific DMARC failures using DMARC analysis and monitoring tools like PowerDMARC. These can help you quickly spot and troubleshoot problems with forwarded or aliased emails.
Test Before Deploying
The smallest of errors can cause issues in authentication and deliverability. Use online tools such as PowerDMARC’s SPF, DKIM, and DMARC checkers to verify your email authentication DNS configurations.
Documentation
Lastly, always keep detailed records of all SPF and DKIM changes. With good documentation, troubleshooting will be much easier. It’s also quite useful for audits or when updating your email setup.
Summing Up
DMARC alias failures often happen due to header misalignment. This can be fixed with regular monitoring, authorizing known intermediaries, as well as using authentication protocols like ARC. Starting with DMARC p=none policy and then gradually moving to p=quarantine and/or p=reject can help you achieve effective DMARC enforcement while avoiding deliverability failures.
If you need expert assistance in getting started with email authentication, we can help! Schedule a free demo today to explore the benefits of PowerDMARC managed email authentication services!
Content Specialist at PowerDMARC
Milena is a skilled writer and content creator with 7+ years of experience in crafting engaging content on IT, cybersecurity, virtual events, and more. She has a proven track record of delivering high-quality work for international magazines and is a graduate of prestigious institutions such as New York University Abu Dhabi, UWC China, and the College of Europe.
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