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Nager.EmailAuthentication

Nager.EmailAuthentication is a .NET library for parsing DMARC, DKIM, and SPF records into structured, easy-to-use data.

  • DMARC (Domain-based Message Authentication, Reporting, and Conformance) enables domain owners to specify how mail receivers should handle emails that fail authentication.
  • DKIM (DomainKeys Identified Mail) adds a cryptographic signature to outgoing emails to ensure their authenticity and integrity.
  • SPF (Sender Policy Framework) specifies which IP addresses are allowed to send email on behalf of a domain.

This library focuses on extracting and interpreting the content of these DNS records, enabling applications to analyze and work with email authentication settings programmatically.

Features

  • Parse DMARC records with comprehensive validation.
  • Parse DKIM Public Key records with comprehensive validation.
  • Parse DKIM Signatures with comprehensive validation.
  • Identify and report errors in DMARC configurations.
  • Identify and report errors in DKIM configurations.

Installation

The package is available on NuGet

PM> install-package Nager.EmailAuthentication

or

dotnet add package Nager.EmailAuthentication

Examples

Parsing a DMARC Record

Use DmarcRecordParser.TryParse to validate a DMARC record string. The method returns true if parsing succeeds and outputs a DmarcRecord object.

var dmarcRecordRaw = "v=DMARC1; p=reject;";
if (!DmarcRecordParser.TryParse(dmarcRecordRaw, out var dmarcRecord))
{
    // dmarcRecord now contains the parsed DMARC policy.
    Console.WriteLine($"DMARC policy: {dmarcRecord.Policy}");
}
else
{
    // Handle unexpected parsing failure (should not happen for a valid record).
}

Handling DMARC Validation Errors

To capture validation errors (e.g., missing or invalid tags), use DmarcRecordDataFragmentParser.TryParse, which provides detailed parsing results when the record is invalid:

var dmarcRecord = "v=DMARC1; p=invalid;";
if (!DmarcRecordDataFragmentParser.TryParse(dmarcRecord, out var dmarcDataFragment, out var parsingResults))
{
    // parseResult contains error messages explaining what went wrong.
    Console.WriteLine("DMARC parsing failed:");
    foreach (var error in parseResult.Errors)
    {
        Console.WriteLine($"  - {error}");
    }
}

Parsing a DKIM Public Key Record

Similarly, you can parse a DKIM public key (DNS TXT) record. Use DkimPublicKeyRecordParser.TryParse and check for errors:

string dkimKeyRecord = "v=DKIM1; p=MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQ..."; // Example public key
if (DkimPublicKeyRecordParser.TryParse(dkimKeyRecord, out var publicKeyRecord))
{
    // publicKeyRecord contains the parsed DKIM public key information.
    Console.WriteLine($"DKIM Key Version: {publicKeyRecord.Version}");
}
else
{
    // Handle invalid DKIM public key record.
    Console.WriteLine("Invalid DKIM public key record.");
}

License

This project is licensed under the MIT License. See the LICENSE file for details.