Where can I find resources to help me understand email headers?
Michael Ko
Co-founder & CEO, Suped
Published 7 Jun 2025
Updated 18 Aug 2025
7 min read
Email headers can seem like a complex jumble of technical terms and codes, especially if you're just starting to delve into email deliverability. However, they are a treasure trove of information, providing a detailed history of an email's journey from sender to recipient. Understanding them is key to diagnosing deliverability issues, identifying spam, or verifying the legitimacy of a sender.
When an email encounters delivery problems, such as landing in the spam folder or not arriving at all, the first place I always look is the email header. It offers insights into authentication results like SPF, DKIM, and DMARC, the servers the email traversed, and even potential spam scores assigned by receiving mailboxes.
While they might appear intimidating at first glance, several resources can help demystify email headers and turn them into powerful diagnostic tools for your email program.
Finding and extracting headers
Before you can interpret email headers, you need to know where to find them. Accessing the full header information varies slightly depending on your email client, but most modern clients offer a way to view the original message or message source. This raw view contains all the metadata. Remember, a common pitfall is viewing only the truncated header, which hides crucial details. Always look for the option to show the full or original message headers.
For Gmail users, open the email, click the three-dot menu next to the reply arrow, and select Show original. For Outlook users, double-click the email to open it in a new window, then go to File > Properties. The headers will be displayed in the Internet headers box. Other email clients will have similar options under menus like View or More options.
Once you have the full headers, you can paste them into an email header analyzer. These tools parse the raw data into a human-readable format, highlighting key fields and providing explanations. This is an invaluable step for beginners and even experienced professionals to quickly make sense of the information.
Understanding key header fields
Email headers are composed of numerous fields, each providing a piece of the puzzle about an email's journey and characteristics. Understanding the most common ones is crucial for effective troubleshooting. I often refer to general guides that explain what each field signifies, such as the Kickbox guide to email headers.
One of the most important fields is Received. This field is added by every server an email passes through, creating a chronological trail from bottom (first server) to top (last server). It includes the IP address of the sending server, the receiving server, and timestamps. By following these, you can trace the exact path your email took and identify any delays, or unexpected routes.
Another crucial header is Authentication-Results, which shows the outcome of email authentication checks like SPF, DKIM, and DMARC. These results directly impact deliverability, as failures can lead to emails being blocked or sent to spam. Pay close attention to pass or fail statuses. If you're seeing failures, it might be an issue with your SPF, DKIM, or DMARC records.
Leveraging online analysis tools
While manual analysis is possible, it can be time-consuming and prone to error. Online email header analyzer tools are indispensable for quickly parsing and making sense of the raw header data. I find them particularly useful for spotting anomalies or understanding complex authentication results. These tools can highlight common issues like DKIM temporary errors or DMARC verification failures.
Many of these tools also provide explanations for each header field and can even flag potential security risks, such as spoofed sender addresses. They are an essential part of my toolkit for identifying the ESP that sent an email or determining Microsoft's spam classification decisions.
Using an email header analyzer
Copy the full header: Ensure you extract the entire raw header, not just the truncated view from your email client.
Paste into analyzer: Use an online tool to parse the header. Google's Messageheader tool is a popular choice, or you can use Mailjet's guide on reading headers.
Review results: Look for red flags like authentication failures, high spam scores, or unexpected server hops.
Remember, email header analyzers do the heavy lifting of parsing, but the true value comes from your ability to interpret the results and relate them to your deliverability goals. Continuously learning about email authentication and deliverability best practices will enhance your ability to leverage this information.
Advanced header analysis and specific insights
Beyond simply reading headers, several advanced concepts and resources can deepen your understanding and analytical skills. For instance, sometimes you need to understand the email sending platform from headers, which often requires looking at specific X-headers or Received lines.
Understanding how email authentication (SPF, DKIM, DMARC) works and how their results are reflected in headers is paramount. A great interactive resource I've come across is learndmarc.com, which provides a hands-on approach to understanding DMARC. Also, for those looking to improve their deliverability rates, understanding how DKIM implementation issues manifest in headers is critical.
I often find that email providers add their own custom headers, usually starting with X-, to provide additional information about how they processed the email. These can include spam scores, virus scan results, or internal routing details. While not standardized, these custom headers (like the X-headers that reveal Microsoft's spam classification) can be very telling about why an email landed where it did. Regularly reviewing these headers can provide valuable clues for improving your sender reputation and deliverability.
For a deeper dive into the technicalities, including how full email headers can reveal delivery delays and other issues, I recommend exploring resources that detail these advanced concepts. Such resources bridge the gap between basic header interpretation and sophisticated troubleshooting.
Views from the trenches
Best practices
Always retrieve the full, raw email header, as truncated views miss critical diagnostic information.
Use online header analyzer tools to quickly parse and visualize complex header data.
Focus on authentication results (SPF, DKIM, DMARC) to pinpoint common deliverability issues.
Trace the 'Received' headers to map the email's journey and identify unusual routing or delays.
Common pitfalls
Overlooking authentication failures in headers, which often lead to emails being marked as spam or blocked.
Ignoring custom X-headers from major ISPs, which can offer valuable clues about email filtering decisions.
Failing to correlate header information with sender reputation metrics, missing a broader deliverability picture.
Using outdated or unreliable header analysis tools that don't provide comprehensive or accurate interpretations.
Expert tips
Consider setting up DMARC reporting, as it provides aggregated XML reports on authentication results directly from receiving mail servers, complementing individual header analysis.
When dealing with emails flagged as spam, compare their headers to those of successfully delivered emails to identify subtle differences in authentication or routing.
Regularly review headers from various ISPs to understand how different providers process and score your emails, helping you adapt sending practices.
If an email is delayed, examine the timestamps in the 'Received' headers to identify precisely where the delay occurred in the delivery chain.
Marketer view
Marketer from Email Geeks says they use the Kickbox blog as a good starting point for understanding email headers. It provides a comprehensive guide on what they are, why they are important, how to read them, and the specific headers to pay attention to.
2023-04-11 - Email Geeks
Expert view
Expert from Email Geeks says that the Certified Senders Alliance (CSA) has a valuable webinar based on the Kickbox blog post, offering a deeper dive into email headers for better deliverability. They mention that a recording is available online, providing a rich, auditory learning experience.
2023-04-11 - Email Geeks
Final thoughts on email headers
Email headers might seem overwhelming initially, but with the right resources and a systematic approach, you can unlock their diagnostic power. They provide the complete story of your email's journey, crucial for understanding and resolving deliverability challenges.
I encourage you to spend time with different header examples and utilize online tools to see how various fields interact. The more you practice reading and interpreting them, the quicker you'll be able to identify the root cause of deliverability issues, whether it's an ISP delay, an authentication failure, or a content-related issue causing your emails to be placed on a blacklist (or blocklist).
By mastering email header analysis, you gain a powerful tool in your email deliverability arsenal, enabling you to proactively monitor and optimize your email campaigns for better inbox placement.
