How to View Full Email Headers in Gmail and Outlook

What Are Email Headers?

Every email contains a hidden section known as the message header. While most email applications only display the sender, recipient, subject, and message body, the header contains detailed technical information about how the email traveled across the internet.

Email headers are one of the most valuable troubleshooting tools available when diagnosing email delivery issues, spam problems, authentication failures, or message routing errors.

Administrators, hosting providers, and email security teams frequently request full email headers when investigating email-related incidents.

Why Email Headers Are Important

Full message headers provide insight into:

• The originating mail server
• Addresses claimed by the sender and recorded by receiving servers
• The recipient address
• Message routing between mail servers
• Delivery timestamps
• Spam filtering results
• SPF authentication results
• DKIM verification results
• DMARC validation status
• Mail server rejection reasons
• Bounce messages and error codes

Without full headers, it is often impossible to accurately determine why a message was delivered, delayed, rejected, or marked as spam.

Information Found in Email Headers

A standard email header may contain fields such as:

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From

The address that appears to have sent the message.

Example:

From: [email protected]

To

The intended recipient.

Example:

To: [email protected]

Subject

The message subject line.

Example:

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Subject: Test Message

Date

The date and time when the message was created.

Example:

Date: Wed, 17 Jun 2026 10:15:22 +0000

Message-ID

A unique identifier assigned to the email.

Example:

Message-ID: <[email protected]>

Received

The most important troubleshooting field.

Each mail server that processes a message adds a new Received entry. Reading these entries helps trace the path the email followed.

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Example:

Received: from mail.example.com

Authentication Results

Many modern mail servers include:

• SPF results
• DKIM results
• DMARC results

Example:

Authentication-Results:
spf=pass
dkim=pass
dmarc=pass

These records help determine whether an email is legitimate or potentially spoofed.

When You Should Collect Full Headers

Full headers are useful when:

• Email delivery fails
• Messages are delayed
• Emails are marked as spam
• Investigating phishing attempts
• Diagnosing SPF failures
• Troubleshooting DKIM issues
• Investigating DMARC rejections
• Analyzing bounce messages
• Verifying message origin

When opening a support ticket regarding email delivery, providing the full header often significantly speeds up troubleshooting.

Viewing Headers in Mozilla Thunderbird

1. Open the message in its own window.
2. Click View in the menu bar.
3. Select Headers.
4. Choose All.

Alternative method:

1. Open the message.
2. Select View.
3. Click Message Source.

The full header will be displayed.

Viewing Headers in Apple Mail (macOS)

1. Open the email in a separate window.
2. Click View.
3. Select Message.
4. Click All Headers.

On older versions of Apple Mail:

1. Open the message.
2. Select Raw Source.

The complete message source and headers will appear.

Viewing Headers in Classic Outlook for Windows

1. Open the message in its own window.
2. Click File.
3. Select Properties.
4. Locate the section labeled Internet Headers.

The complete header information is displayed in the text box.

Viewing Headers in New Outlook and Outlook.com

Open the message and choose More actions at the top of the message window, then View and View message details. Copy the complete header from that panel. In classic Outlook for Windows, open the message in its own window and use File, Properties, Internet headers.

Viewing Headers in Gmail

1. Open the email.
2. Click the three-dot menu near the Reply button.
3. Select Show Original.

Gmail will display:

• Complete message headers
• SPF results
• DKIM results
• DMARC results
• Original message source

You can also download the original message if needed.

Viewing Headers in Yahoo Mail

1. Open the email.
2. Click More above the message.
3. Select View Full Header.

The complete header information will appear.

Viewing Headers in Horde Webmail

1. Open the email.
2. Click Show All Headers.

On newer versions:

1. Open the preview pane.
2. Click Other Options.
3. Select View Source.

The complete message source will be displayed.

Viewing Headers in Roundcube Webmail

1. Open the email.
2. Click Message Source.

In newer versions:

1. Locate the small arrow icon in the message header area.
2. Click the icon.
3. Select Toggle Raw Message Headers.

The complete headers will become visible.

Viewing Headers in SquirrelMail

1. Open the email.
2. Locate the Options section.
3. Click View Full Header.

The complete header information will be displayed.

Understanding Email Routing with Received Headers

Read the route from bottom to top, but establish trust from your own receiving system downward. A sender can forge earlier Received or Authentication-Results lines. A passing authentication result authenticates a domain or signature; it does not prove that the content is safe or the sender is trustworthy.

Each mail server adds a new Received line.

Example:

Received: from mail1.example.com
Received: from relay.provider.net
Received: from mx.recipient.com

To trace the message path correctly:

• Read Received headers from bottom to top.
• The oldest entry is usually the originating server.
• The newest entry is typically the recipient’s mail server.

This allows administrators to identify where delays or failures occurred.

Common Authentication Results

SPF Pass

spf=pass

The sending server was authorized to send email for the domain.

SPF Fail

spf=fail

The sender was not authorized by the domain’s SPF record.

DKIM Pass

dkim=pass

The message signature was successfully verified.

DKIM Fail

dkim=fail

The message signature could not be validated.

DMARC Pass

dmarc=pass

The message passed SPF or DKIM with alignment to the visible From domain.

DMARC Fail

dmarc=fail

Neither SPF nor DKIM produced an aligned pass; the recipient applies its handling policy, which may include quarantine or rejection.

How to Share Headers Safely

When providing headers to a support team:

1. Copy the entire header section.
2. Include any bounce messages.
3. Include the delivery timestamp.
4. Include the sender and recipient addresses involved.

Send complete headers only through the trusted support channel. For public posts, redact addresses and other sensitive information, while keeping an unmodified private copy for investigation.

Final Notes

Full email headers provide detailed information about how a message was processed, authenticated, and delivered. They are essential when diagnosing delivery failures, spam classification issues, authentication errors, and mail server rejections.

Whether you use Outlook, Gmail, Apple Mail, Thunderbird, Horde, Roundcube, or another email platform, learning how to access full headers can significantly improve your ability to troubleshoot email-related problems and provide useful information to support teams.