What is an Email Header?

This article will pull back the curtain on email headers. We’ll explore what they are, why they’re incredibly important for you and your clients, and how you can use them to become an email detective, ensuring smoother, more reliable communication.

Peeling Back the Layers: What Exactly is an Email Header?

When you open an email, you typically see the sender’s name, the recipient, the subject, and the date. This is the visible part of the email, designed for human eyes. But behind the scenes, every email carries an email header, a detailed block of metadata that’s not usually displayed by default.

Think of an email like a traditional letter. The body of the email is the letter itself. The email header, on the other hand, is like the envelope combined with all the post office stamps and routing information it collects during its journey. It contains crucial details about the email’s origin, its path through various mail servers, and how it was authenticated.

This metadata is primarily for email servers and software to understand how to handle the message, verify its legitimacy, and decide where it should go – inbox, spam, or somewhere else. But for those of us who build and manage websites that send emails, or who help clients with their email marketing, these headers are invaluable diagnostic tools.

Summary: An email header is a code snippet containing technical details about an email’s journey and sender. It’s the email’s digital passport and travel log, all rolled into one.

Why Email Headers Matter to You (and Your Clients): The Practical Benefits

You might be thinking, “Okay, it’s technical data, but why should I, as a web creator, care?” Fair question! Understanding email headers offers several practical advantages, especially when you’re responsible for websites that rely on email communication – from contact forms to e-commerce notifications to full-blown marketing campaigns.

• Troubleshooting Email Delivery Issues: This is probably the most significant benefit. When emails aren’t getting delivered, or they’re landing in spam, the header often holds the clues. It can show you where the email got stuck, if it was rejected by a server, or why a spam filter flagged it. This information is gold when a client says, “My contact form emails aren’t coming through!”
• Verifying Email Authenticity & Spotting Phishing/Spoofing: Email headers can help you determine if an email is genuinely from the person or organization it claims to be from. By examining specific fields, you can spot inconsistencies that might indicate a phishing attempt or a spoofed email, helping protect your clients and their customers.
• Understanding Email Paths & Delays: Ever wondered why an email took so long to arrive? The Received headers trace the email’s journey from server to server, including timestamps. This can help pinpoint where delays occurred in the delivery chain.
• Ensuring Marketing Campaign Effectiveness: For clients running email marketing campaigns (perhaps using a toolkit integrated into their WordPress site), deliverability is everything. Headers provide insights into authentication (SPF, DKIM, DMARC), which are critical factors for getting emails into the inbox. Understanding these helps ensure campaigns have the best chance of success.
• Compliance and Auditing: In some cases, email headers can serve as a record for compliance purposes, providing a trail of communication.

Knowing how to access and interpret email headers moves you from just building sites to being a more effective technical consultant for your clients, especially when email problems arise. This capability enhances the value you provide, reinforcing your role as a knowledgeable professional.

Summary: Email headers aren’t just for sysadmins. For web creators, they are key to diagnosing delivery problems, enhancing security, and ensuring client communications are effective.

Dissecting the Digital Envelope: Common Email Header Fields Explained

Email headers are composed of various fields, each providing a specific piece of information. While the sheer amount of data can look intimidating at first, understanding a few key fields will get you a long way. Let’s break down some of the most common and important ones:

• From:

• What it is: Shows the sender’s email address and often their display name.
• Significance: This is what the recipient sees as the sender. However, be aware that the display name and even the email address can sometimes be spoofed in simple phishing attempts. More advanced checks (like DKIM/SPF) are needed for true verification.
• To: / Cc: / Bcc:

• What they are: To: lists the primary recipient(s). Cc: (Carbon Copy) lists other recipients who also receive the email. Bcc: (Blind Carbon Copy) lists recipients who receive the email without other recipients knowing.
• Significance: Bcc: information is typically stripped from the headers received by other To: and Cc: recipients to maintain privacy. The receiving server of a Bcc: recipient will know they received it.
• Subject:

• What it is: The topic of the email, as entered by the sender.
• Significance: A standard, visible part, but also present in the header.
• Date:

• What it is: The date and time the email was composed and sent from the originating email client.
• Significance: Useful for sequencing events, but keep in mind time zone differences and the fact that this is set by the sender’s computer, which could theoretically be incorrect.
• Return-Path: (also known as Envelope From, Reverse Path, or MAIL FROM)

• What it is: This is a crucial one! It specifies the email address where bounce messages (non-delivery reports or NDRs) should be sent if the email fails to reach its destination.
• Significance: This address is used during the SMTP (Simple Mail Transfer Protocol) session. It might be different from the display From: address. For email deliverability and list hygiene, managing bounces effectively via the Return-Path is vital. Email service providers often use this to manage bounce information.
• Reply-To:

• What it is: An optional field that specifies the email address to which replies should be sent.
• Significance: If present, when a recipient clicks “Reply,” their email client will use this address instead of the From: address. Useful if you want replies to go to a different mailbox (e.g., [email protected] instead of a specific marketing campaign address).
• Message-ID:

• What it is: A globally unique string of characters generated by the initial sending mail server (or sometimes the email client) to identify that specific email message.
• Significance: Essential for tracking individual emails, correlating replies (In-Reply-To and References headers use Message-IDs), and troubleshooting. No two legitimate emails should have the same Message-ID.
• Received:

• What it is: This is perhaps the most complex but most informative field for tracing an email’s journey. Each mail server (Mail Transfer Agent or MTA) that handles the email adds a Received: line to the top of the header block.
• Significance: By reading the Received: lines from bottom to top, you can trace the path an email took from the sender to the recipient. You can see which servers it passed through, their IP addresses, and the timestamp for each hop. This is invaluable for identifying delivery delays or points of failure. Multiple Received: lines are normal.
• Authentication-Results:

• What it is: This header is added by a receiving mail server and shows the results of email authentication checks like SPF, DKIM, and DMARC.
• Significance: Absolutely critical for deliverability!

• SPF (Sender Policy Framework): Verifies that the sending mail server’s IP address is authorized to send emails for the From: domain.
• DKIM (DomainKeys Identified Mail): Adds a digital signature to the email. This allows the receiver to verify that the email originated from the claimed domain and hasn’t been tampered with in transit.
• DMARC (Domain-based Message Authentication, Reporting, and Conformance): Tells receiving servers what to do if an email fails SPF or DKIM checks (e.g., quarantine it, reject it, or do nothing) and allows for reporting.
• A pass here is good; a fail or softfail can lead to spam folder placement or rejection. As a web creator, you might help clients set up the necessary DNS records (TXT records) for SPF, DKIM, and DMARC for their domain.
• X-Spam-Status: / X-Spam-Level: / X-Spam-Flag:

• What they are: These are custom headers (see X-Headers below) often added by spam filtering software (like SpamAssassin) on receiving servers.
• Significance: They indicate whether the email was considered spam, often providing a score or a YES/NO flag. If an email is being incorrectly flagged, these headers can offer clues as to why.
• X-Mailer: / User-Agent:

• What they are: These non-standard headers often indicate the email client software (e.g., Microsoft Outlook, Apple Mail, Thunderbird) or the system (e.g., a specific marketing platform) used to send the email.
• Significance: Can sometimes be useful for diagnosing issues related to a specific sending application.
• Other X-Headers: (Custom Headers)

• What they are: Any header field starting with “X-” is a custom, non-standard header. Email systems and applications can add these for various purposes, like internal tracking, routing instructions, or specific application data.
• Significance: Their meaning depends on the system that added them. Some ESPs use X-headers to track campaign IDs or list IDs.

Understanding these fields allows you to start making sense of the seemingly cryptic information in an email header. It’s like learning the key symbols on a map – once you know them, navigation becomes much easier.

How to View Full Email Headers: A Step-by-Step Guide

Now that you know what email headers are, how do you actually see them? Most email clients hide them by default because they’re not needed for everyday reading. Here’s how to unearth them in some popular clients:

Important Note: The exact menu names and steps can vary slightly with software updates, but the general approach is similar.

1. Gmail (Web):

• Open the email you want to inspect.
• Click the three vertical dots (More menu) in the top-right corner of the email pane (next to the reply arrow).
• Select “Show original.”
• A new browser tab or window will open, displaying the full raw message source, including all headers at the top. You’ll see options to “Copy to clipboard” or “Download Original.”

2. Microsoft Outlook (Desktop App – Windows & Mac):

• Open the email by double-clicking it to view it in its own window.
• Click on the File tab in the Outlook ribbon.
• Choose Properties.
• In the Properties dialog box, the full email headers are displayed in the “Internet headers” box at the bottom. You may need to scroll within this box to see everything. You can select the text and copy it.

3. Microsoft Outlook (Web – Outlook.com / Microsoft 365 Web Access):

• Open the email.
• Click the three horizontal dots (More actions) in the email message pane (usually to the right of the sender details).
• Navigate to View -> View message details (or sometimes “View message source”).
• A pane or new window will appear showing the raw message source with headers.

4. Apple Mail (on macOS):

• Open the email.
• From the menu bar at the top of your screen, click View.
• Go to Message -> All Headers (or Raw Source).
• The headers will appear above the email body in the same window.

5. Mozilla Thunderbird:

• Open the email.
• From the menu bar, click View -> Headers -> All.
• Alternatively, you can press Ctrl+U (on Windows/Linux) or Cmd+U (on Mac) to view the full message source, which includes the headers.

What about mobile email clients?

Viewing full email headers on mobile devices is often more challenging or not supported directly within the app. If you need to inspect headers, it’s usually best to access the email through a desktop client or webmail interface.

Once you’ve accessed the headers, you can copy and paste them into a text editor for easier reading or into an online email header analysis tool.

Quick Tip: When you first look at raw headers, they can seem like a wall of text. Don’t be intimidated! Focus on finding the key fields we discussed earlier.

Reading the Tea Leaves: Basic Email Header Analysis for Troubleshooting

Okay, you’ve got the headers in front of you. Now what? Let’s look at some common troubleshooting scenarios for web creators and how to analyze headers to find answers.

Scenario 1: Spotting a Phishing Attempt or Spoofed Email

Your client forwards you a suspicious email that looks like it’s from their bank, but something feels off.

• Check the From: vs. Return-Path: vs. Reply-To::

• Does the display From: name match the actual email address? Sometimes attackers will use a familiar name but the email address will be completely unrelated (e.g., “Your Bank” <[email protected]>).
• Is the Return-Path: or Reply-To: address different from the From: address and pointing to an unexpected domain? This is a common tactic so that replies go to the attacker.
• Examine Received: Headers:
• Are the originating servers from unexpected geographic locations or domains that don’t match the purported sender? For example, an email supposedly from a US bank originating from servers in a completely different country is a red flag. Read these from bottom to top.
• Look at Authentication-Results::

• Did SPF, DKIM, or DMARC checks fail? This is a strong indicator of a spoofed email. Legitimate organizations usually have these set up correctly.
• spf=fail, dkim=fail, or dmarc=fail are big warnings.

Scenario 2: Tracing an Email’s Journey (and Delays)

A client complains that emails from their website’s contact form are taking hours to arrive.

• Analyze the Received: Headers:

• Remember, each server that handles the email adds a Received: line at the top of the existing headers. To trace the path chronologically, read them from the bottom up.
• Each Received: line should have a timestamp. Compare the timestamps between hops. Large gaps between timestamps on consecutive Received: lines indicate a delay at that particular server.
• This can help you determine if the delay is with the sending server (e.g., your web server), an intermediary server, or the recipient’s mail server.

Scenario 3: Checking Email Authentication (SPF, DKIM, DMARC)

Your client’s newsletters are frequently landing in spam folders. You suspect an authentication issue.

• Find the Authentication-Results: Header: This is your go-to.
• SPF: Look for something like spf=pass, spf=fail, spf=softfail, or spf=neutral. A pass means the sending IP is authorized for the domain in the Return-Path. A fail or softfail is problematic.
• Why it matters for web creators: Clients often use third-party services to send emails (marketing platforms, transactional email services, even WordPress via plugins). Their domain’s SPF record needs to include these services as authorized senders. You might need to help them update their DNS TXT records.
• DKIM: Look for dkim=pass or dkim=fail. A pass means the email’s signature is valid and it hasn’t been tampered with. A fail indicates a problem with the signature or that the email was altered.
• Why it matters for web creators: DKIM also requires a DNS TXT record containing a public key, which aligns with a private key used by the sending server/service. You may assist clients in setting this up.
• DMARC: Look for dmarc=pass or dmarc=fail. DMARC aligns SPF and DKIM results with the From: domain and tells receivers what policy to apply (none, quarantine, reject) if checks fail.
• Why it matters for web creators: Implementing DMARC is a best practice for protecting a domain from spoofing and improving deliverability. Setting up a DMARC policy (another DNS TXT record) is something clients will likely need help with.

If you see failures in these authentication checks, it’s a strong clue that you need to work with your client to correct their DNS records or the configuration of their sending service. This proactive step can significantly improve their email deliverability – a huge win for any client relying on email.

Scenario 4: Identifying Why an Email Was Marked as Spam

If an email lands in spam, headers often provide clues.

• Look for X-Spam-Status:, X-Spam-Level:, or similar X- headers.

• These headers, added by spam filters, might explicitly say “Yes” for spam status, or provide a numerical score (higher scores often mean more likely to be spam).
• They might also list the specific rules or tests the email failed (e.g., “contains suspicious URL,” “failed SPF check,” “known spammer IP”). This can guide you on what to fix.

Using Online Header Analysis Tools:

Manually reading headers can be tedious. Several free online tools can help parse email headers and present the information in a more human-readable format. Simply copy the full raw header and paste it into one of these tools. Popular options include Google Admin Toolbox Messageheader, MXToolbox Email Header Analyzer, and Microsoft’s Message Header Analyzer.

These tools can quickly highlight important information like the delivery path, authentication results, and spam scores, saving you time.

Summary: Analyzing email headers involves looking for inconsistencies in sender information, tracing the delivery path via Received: lines, and critically examining Authentication-Results for SPF, DKIM, and DMARC. This detective work is invaluable for solving common email problems.

Email Headers and Your Client’s Email Deliverability

For any client who uses email for marketing, sales, or even basic transactional messages (like order confirmations or password resets from their WordPress site), email deliverability is paramount. Emails that don’t reach the inbox are wasted effort and lost opportunities. Email headers are intrinsically linked to deliverability.

• Authentication is Key: As we’ve discussed, proper SPF, DKIM, and DMARC setup (verified in the Authentication-Results: header) is no longer optional; it’s essential. Major mailbox providers like Gmail and Yahoo are increasingly strict about these. Emails failing these checks are highly likely to be filtered as spam or rejected outright. As a web creator, guiding your clients to correctly configure these DNS records for their sending domain (and any third-party services sending on their behalf) is a critical service.
• Server Reputation: While not always directly visible in a single header field, the IP addresses listed in the Received: headers are associated with sender reputations. If a client is sending from a shared web server with a poor IP reputation (due to other users on that server sending spam), their emails can suffer. This is why dedicated IP addresses or reputable Email Service Providers (ESPs) are often recommended for significant email volumes.
• Content and Engagement (Indirectly Indicated): While headers don’t show content quality directly, X-Spam- headers reflect how spam filters perceive the content in conjunction with other factors. High spam scores can relate to content, sender reputation, and authentication status.
• The Role of Email Service Providers (ESPs): Reputable ESPs (whether for marketing campaigns or transactional emails) work hard to manage the technical aspects that influence headers and deliverability. They correctly implement authentication, manage IP reputations, and ensure headers are well-formed. Using a quality ESP often means many of these header-related best practices are handled for your client.

When you help a client set up a new website or an email marketing system (perhaps one that integrates smoothly with WordPress, like a comprehensive communication toolkit), ensuring their email sending practices are sound from a technical perspective (including authentication) is vital. Explaining the “why” behind these setups, even if you’re using a tool that simplifies the “how,” positions you as a more knowledgeable and valuable partner.

Summary: Proper email authentication, reflected in headers, directly impacts deliverability. Web creators can play a crucial role in helping clients set up SPF, DKIM, and DMARC, or choose services that manage these well, ensuring emails reach the inbox.

Limitations and Considerations When Working with Email Headers

While incredibly useful, it’s also important to acknowledge a few limitations when dealing with email headers:

• Technical Complexity: Let’s be honest, raw email headers can look like a foreign language at first. It takes a bit of learning to navigate them and understand what’s important. This is where analysis tools can really help.
• Information Overload: Headers contain a lot of data. Not all of it is relevant to every troubleshooting scenario. The key is to focus on the actionable fields like Received:, Authentication-Results:, Return-Path:, and any spam-related X- headers.
• X-Headers are Non-Standard: While many X- headers are common (like those from SpamAssassin), their presence and meaning can vary wildly between email systems. Don’t assume an X-Header means the same thing everywhere.
• Not a Crystal Ball: Headers tell you a lot about an email’s journey and technical handling, but they don’t tell you everything. They won’t explain why a recipient didn’t open an email if it was delivered, or why your content wasn’t persuasive.

Despite these points, the insights gained from even a basic understanding of email headers far outweigh the initial learning curve, especially when you’re trying to solve a frustrating email problem.

Empowering Your Email Strategy: The Bigger Picture

Understanding email headers is crucial for web creators to offer better client support and build robust communication systems. While modern platforms simplify email sending, header knowledge empowers you to diagnose issues beyond standard tools, advise clients on email best practices, and communicate effectively with hosting and ESP support.

Email headers reveal the journey and “health” of an email, aiding in ensuring reliable contact form submissions, newsletter delivery, and e-commerce notifications. This insight builds client trust by demonstrating a deeper understanding of the underlying email technology. Ultimately, mastering email headers elevates your service from basic web development to providing comprehensive digital solutions, enhancing your clients’ online communication success.