Raw email headers lint

Raw Email Headers Lint helps you inspect pasted email header blocks for common formatting problems before you rely on them for troubleshooting, parsing, or forensic review. It unfolds folded header lines, then checks for issues such as missing colons, empty values, and duplicate fields. This is useful for developers, support teams, deliverability analysts, and anyone working with raw message source who needs a quick sanity check on header structure. Because email headers are often copied from logs, tickets, or mailbox tools, small formatting mistakes can make them hard to parse or misread. This validator helps surface those problems early so you can review the header block more confidently.

How This Validator Works

This tool examines raw email header text line by line and applies basic structural checks. It first unfolds continuation lines so multi-line headers can be read as a single field. Then it looks for header lines that do not contain a colon separator, headers with no value after the colon, and repeated header names that may indicate duplication or malformed input. The goal is not to rewrite the message, but to highlight likely formatting issues that could affect parsing, debugging, or downstream processing.

• Unfolds headers that span multiple lines
• Flags lines missing the required name: value structure
• Detects empty header values
• Identifies duplicate header fields for review

Common Validation Errors

• Missing colon separator — a header line is present, but it is not written in standard Field-Name: Field-Value format.
• Empty value — the header name exists, but nothing appears after the colon.
• Duplicate header — the same field appears more than once when it is expected to be unique or reviewed carefully.
• Improper folding — continuation lines may not be indented or may be broken in a way that makes the header hard to parse.
• Unexpected formatting — extra spacing, stray characters, or pasted content from message bodies can make the header block inconsistent.

Where This Validator Is Commonly Used

• Email debugging — reviewing raw headers from support cases or delivery investigations
• Deliverability analysis — checking message metadata before deeper SPF, DKIM, or DMARC review
• Help desk workflows — validating copied header blocks from users or internal teams
• Security triage — inspecting message source during phishing or spoofing investigations
• Developer tooling — testing parsers, ingestion pipelines, or email-processing scripts
• QA and data cleanup — confirming that exported header data is structurally consistent

Why Validation Matters

Email headers contain important metadata such as routing information, message identifiers, timestamps, authentication results, and client details. If the header block is malformed, tools may fail to parse it correctly or may produce incomplete results. Validating the structure first helps reduce confusion during troubleshooting and makes it easier to compare messages across systems. It also supports more reliable downstream analysis when headers are used in logs, support tickets, or security reviews.

Technical Details

• Input type: raw email header text
• Primary format expectation: RFC-style header fields using name: value syntax
• Normalization: folded lines are unfolded before checks are applied
• Checks performed: missing colons, empty values, duplicate fields
• Scope: structural linting, not full email authentication or message-content analysis

FAQ

What are raw email headers?

Raw email headers are the metadata lines at the top of a message source. They include fields such as From, To, Subject, Date, and technical routing or authentication information. These headers help mail systems and analysts understand how a message was handled and where it came from.

What does “unfolding” headers mean?

Unfolding means combining header lines that were split across multiple lines for readability or transport. In standard email formatting, a continuation line begins with whitespace and belongs to the previous header field. Unfolding makes the header easier to inspect and helps validators read it as one logical value.

Why would a header be missing a colon?

A missing colon usually means the header was copied incorrectly, edited manually, or corrupted during export. Since email headers normally use Field-Name: Field-Value syntax, a line without a colon may not be parsed as a valid header and can cause downstream tools to skip or misread it.

Are duplicate headers always wrong?

Not always. Some email fields can appear more than once in certain contexts, but duplicates are often worth reviewing because they may indicate malformed input, copied content, or unexpected message structure. This validator flags duplicates so you can decide whether they are intentional or a sign of a problem.

Does this tool check SPF, DKIM, or DMARC?

No. This validator focuses on header structure, not email authentication. SPF, DKIM, and DMARC require different checks that examine DNS records, signatures, and alignment rules. Raw header linting is useful as a first step before deeper deliverability or security analysis.

Can this help with phishing investigations?

Yes, it can help at the structural review stage. Raw headers often provide clues about routing, sender infrastructure, and message handling. While this tool does not determine whether a message is malicious, it can make header data easier to inspect before you compare it with authentication results and other indicators.

What should I do if the header block looks malformed?

First, confirm that you pasted only the raw header section and not the message body. Then check for broken lines, missing separators, or accidental edits from copying. If the source came from a mailbox client or ticketing system, try exporting the full message source again to preserve the original formatting.

Is this validator useful for developers?

Yes. Developers often use raw header linting when building parsers, email ingestion pipelines, support tools, or message analysis workflows. It helps catch formatting issues early, especially when testing how software handles real-world header data that may be incomplete or inconsistently copied.

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• DNS Checker — reviews domain and DNS-related records
• SPF Checker — evaluates sender policy configuration
• DKIM Checker — inspects email signature setup
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