Email headers are code snippets in any email containing various information about the sender, recipient, email MTA route or details. All email headers always precede the email body.
Why would you care about email headers?
Email headers are an important part of your email marketing, even though you as a marketer do not interact directly with them.
They have an important role in deliverability, email authentication and in the technical communication between systems.
Email headers are represented by key value pairs, where key represents the name of the header and value… well, the value for that name.
Roles & benefits of headers added to outgoing emails
- provide information about the sender and the recipient
- prevents spam by authenticating the sender of the email
- help identify the email route by telling MTAs (Mail Transfer Agents) where to direct the email to. Each MTA adds a bit more information to the message and the time it was received and forwarded.
Most important email headers
While there are quite many possible email headers that systems will add automatically (or you can do it yourself, maybe without even knowing it), the most important ones are the following:
- To
- From
- Body
- Subject
- Reply-To
- Content-Type
- CC and Bcc (Carbon Copy and Blind Carbon Copy)
- DKIM-Signature
- Received-SPF
- Priority
- Encoding
- Encrypted
How to view email headers?
Head over to your email client. Let’s say this is Gmail.
Click the 3 dots on the right side of every message and select Show original.
A text list like the following will show up on the screen.
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Full List of email headers
| Header Name | Protocol | Status |
| Accept-Language | ||
| Alternate-Recipient | ||
| Archived-At | standard | |
| Authentication-Results | standard | |
| Auto-Submitted | standard | |
| Autoforwarded | ||
| Autosubmitted | ||
| Bcc | standard | |
| Body | none | reserved |
| Cc | standard | |
| Comments | standard | |
| Content-Alternative | MIME | |
| Content-Description | MIME | |
| Content-Disposition | MIME | |
| Content-Duration | MIME | |
| Content-features | MIME | |
| Content-ID | MIME | |
| Content-Identifier | ||
| Content-Language | MIME | |
| Content-Location | MIME | |
| Content-MD5 | MIME | |
| Content-Return | ||
| Content-Transfer-Encoding | MIME | |
| Content-Translation-Type | MIME | standard |
| Content-Type | MIME | |
| Conversion | ||
| Conversion-With-Loss | ||
| DL-Expansion-History | ||
| Date | standard | |
| Deferred-Delivery | ||
| Delivery-Date | ||
| Discarded-X400-IPMS-Extensions | ||
| Discarded-X400-MTS-Extensions | ||
| Disclose-Recipients | ||
| Disposition-Notification-Options | ||
| Disposition-Notification-To | ||
| DKIM-Signature | standard | |
| Encoding | ||
| Encrypted | ||
| Expires | ||
| Expiry-Date | ||
| From | standard | |
| Generate-Delivery-Report | ||
| Importance | ||
| In-Reply-To | standard | |
| Incomplete-Copy | ||
| Keywords | standard | |
| Language | ||
| Latest-Delivery-Time | ||
| List-Archive | ||
| List-Help | ||
| List-ID | ||
| List-Owner | ||
| List-Post | ||
| List-Subscribe | ||
| List-Unsubscribe | ||
| List-Unsubscribe-Post | standard | |
| Message-Context | ||
| Message-ID | standard | |
| Message-Type | ||
| MMHS-Exempted-Address | ||
| MMHS-Extended-Authorisation-Info | ||
| MMHS-Subject-Indicator-Codes | ||
| MMHS-Handling-Instructions | ||
| MMHS-Message-Instructions | ||
| MMHS-Codress-Message-Indicator | ||
| MMHS-Originator-Reference | ||
| MMHS-Primary-Precedence | ||
| MMHS-Copy-Precedence | ||
| MMHS-Message-Type | ||
| MMHS-Other-Recipients-Indicator-To | ||
| MMHS-Other-Recipients-Indicator-CC | ||
| MMHS-Acp127-Message-Identifier | ||
| MMHS-Originator-PLAD | ||
| MT-Priority | standard | |
| Obsoletes | ||
| Organization | informational | |
| Original-Encoded-Information-Types | ||
| Original-From | standard | |
| Original-Message-ID | ||
| Original-Recipient | standard | |
| Originator-Return-Address | ||
| Original-Subject | standard | |
| PICS-Label | ||
| Prevent-NonDelivery-Report | ||
| Priority | ||
| Received | standard | |
| Received-SPF | standard | |
| References | standard | |
| Reply-By | ||
| Reply-To | standard | |
| Require-Recipient-Valid-Since | standard | |
| Resent-Bcc | standard | |
| Resent-Cc | standard | |
| Resent-Date | standard | |
| Resent-From | standard | |
| Resent-Message-ID | standard | |
| Resent-Sender | standard | |
| Resent-To | standard | |
| Return-Path | standard | |
| Sender | standard | |
| Sensitivity | ||
| Solicitation | ||
| Subject | standard | |
| Supersedes | ||
| TLS-Report-Domain | standard | |
| TLS-Report-Submitter | standard | |
| TLS-Required | standard | |
| To | standard | |
| VBR-Info | standard | |
| X400-Content-Identifier | ||
| X400-Content-Return | ||
| X400-Content-Type | ||
| X400-MTS-Identifier | ||
| X400-Originator | ||
| X400-Received | ||
| X400-Recipients | ||
| X400-Trace |
If you want to analyze email headers you can use this tool from Google. It can help you:
- detect delivery delays
- aproximative source of the delay
- responsible of the delay.
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