Authentication Results

VaultSandbox validates email authentication for every received email, providing detailed SPF, DKIM, DMARC, and reverse DNS results.

What is Email Authentication?

Email authentication helps verify that an email:

Came from the claimed sender domain (SPF)
Wasn’t modified in transit (DKIM)
Complies with the domain’s policy (DMARC)
Came from a legitimate mail server (Reverse DNS)

AuthResults Struct

Every email has an AuthResults field:

email, err := inbox.WaitForEmail(ctx, vaultsandbox.WithWaitTimeout(10*time.Second))
if err != nil {
    log.Fatal(err)
}

auth := email.AuthResults

fmt.Printf("SPF: %+v\n", auth.SPF)
fmt.Printf("DKIM: %+v\n", auth.DKIM)
fmt.Printf("DMARC: %+v\n", auth.DMARC)
fmt.Printf("ReverseDNS: %+v\n", auth.ReverseDNS)

The AuthResults struct is defined in the authresults package:

import "github.com/vaultsandbox/client-go/authresults"

type AuthResults struct {
    SPF        *SPFResult
    DKIM       []DKIMResult
    DMARC      *DMARCResult
    ReverseDNS *ReverseDNSResult
}

SPF (Sender Policy Framework)

Verifies the sending server is authorized to send from the sender’s domain.

SPFResult Struct

type SPFResult struct {
    Result string // "pass", "fail", "softfail", "neutral", "none", "temperror", "permerror"
    Domain string
    IP     string
    Info   string
}

if email.AuthResults.SPF != nil {
    spf := email.AuthResults.SPF
    fmt.Printf("Result: %s\n", spf.Result)
    fmt.Printf("Domain: %s\n", spf.Domain)
    fmt.Printf("Info: %s\n", spf.Info)
}

SPF Status Values

Status	Meaning
`pass`	Sending server is authorized
`fail`	Sending server is NOT authorized
`softfail`	Probably not authorized (policy says ~all)
`neutral`	Domain makes no assertion
`temperror`	Temporary error during check
`permerror`	Permanent error in SPF record
`none`	No SPF record found

SPF Example

email, err := inbox.WaitForEmail(ctx, vaultsandbox.WithWaitTimeout(10*time.Second))
if err != nil {
    t.Fatal(err)
}

if email.AuthResults.SPF != nil {
    spf := email.AuthResults.SPF

    if spf.Result != "pass" {
        t.Errorf("expected SPF pass, got %s", spf.Result)
    }
    if spf.Domain != "example.com" {
        t.Errorf("expected domain example.com, got %s", spf.Domain)
    }

    fmt.Printf("SPF %s for %s\n", spf.Result, spf.Domain)
}

DKIM (DomainKeys Identified Mail)

Cryptographically verifies the email hasn’t been modified and came from the claimed domain.

DKIMResult Struct

type DKIMResult struct {
    Result   string // "pass", "fail", "none"
    Domain   string
    Selector string
    Info     string
}

dkim := email.AuthResults.DKIM // []DKIMResult

if len(dkim) > 0 {
    for _, result := range dkim {
        fmt.Printf("Result: %s\n", result.Result)
        fmt.Printf("Domain: %s\n", result.Domain)
        fmt.Printf("Selector: %s\n", result.Selector)
        fmt.Printf("Info: %s\n", result.Info)
    }
}

Note: An email can have multiple DKIM signatures (one per signing domain).

DKIM Status Values

Status	Meaning
`pass`	Signature is valid
`fail`	Signature is invalid
`none`	No DKIM signature found

DKIM Example

email, err := inbox.WaitForEmail(ctx, vaultsandbox.WithWaitTimeout(10*time.Second))
if err != nil {
    t.Fatal(err)
}

if len(email.AuthResults.DKIM) > 0 {
    dkim := email.AuthResults.DKIM[0]

    if dkim.Result != "pass" {
        t.Errorf("expected DKIM pass, got %s", dkim.Result)
    }
    if dkim.Domain != "example.com" {
        t.Errorf("expected domain example.com, got %s", dkim.Domain)
    }

    fmt.Printf("DKIM %s (%s._domainkey.%s)\n", dkim.Result, dkim.Selector, dkim.Domain)
}

DMARC (Domain-based Message Authentication)

Checks that SPF or DKIM align with the From address and enforces the domain’s policy.

DMARCResult Struct

type DMARCResult struct {
    Result  string // "pass", "fail", "none"
    Policy  string // "none", "quarantine", "reject"
    Aligned bool
    Domain  string
    Info    string
}

if email.AuthResults.DMARC != nil {
    dmarc := email.AuthResults.DMARC
    fmt.Printf("Result: %s\n", dmarc.Result)
    fmt.Printf("Domain: %s\n", dmarc.Domain)
    fmt.Printf("Policy: %s\n", dmarc.Policy)
    fmt.Printf("Aligned: %v\n", dmarc.Aligned)
    fmt.Printf("Info: %s\n", dmarc.Info)
}

DMARC Status Values

Status	Meaning
`pass`	DMARC check passed (SPF or DKIM aligned)
`fail`	DMARC check failed
`none`	No DMARC policy found

DMARC Policies

Policy	Meaning
`none`	No action (monitoring only)
`quarantine`	Treat suspicious emails as spam
`reject`	Reject emails that fail DMARC

DMARC Example

email, err := inbox.WaitForEmail(ctx, vaultsandbox.WithWaitTimeout(10*time.Second))
if err != nil {
    t.Fatal(err)
}

if email.AuthResults.DMARC != nil {
    dmarc := email.AuthResults.DMARC

    if dmarc.Result != "pass" {
        t.Errorf("expected DMARC pass, got %s", dmarc.Result)
    }
    if dmarc.Domain != "example.com" {
        t.Errorf("expected domain example.com, got %s", dmarc.Domain)
    }

    fmt.Printf("DMARC %s (policy: %s)\n", dmarc.Result, dmarc.Policy)
}

Reverse DNS

Verifies the sending server’s IP resolves to a hostname that matches the sending domain.

ReverseDNSResult Struct

type ReverseDNSResult struct {
    Verified bool   // true if reverse DNS verified
    IP       string
    Hostname string
    Info     string
}

if email.AuthResults.ReverseDNS != nil {
    rdns := email.AuthResults.ReverseDNS
    fmt.Printf("Verified: %v\n", rdns.Verified)
    fmt.Printf("IP: %s\n", rdns.IP)
    fmt.Printf("Hostname: %s\n", rdns.Hostname)
    fmt.Printf("Info: %s\n", rdns.Info)
}

Reverse DNS Verified Values

Verified	Meaning
`true`	Reverse DNS verified
`false`	Reverse DNS failed

Reverse DNS Example

email, err := inbox.WaitForEmail(ctx, vaultsandbox.WithWaitTimeout(10*time.Second))
if err != nil {
    t.Fatal(err)
}

if email.AuthResults.ReverseDNS != nil {
    rdns := email.AuthResults.ReverseDNS

    fmt.Printf("Reverse DNS: %s -> %s\n", rdns.IP, rdns.Hostname)
    fmt.Printf("Verified: %v\n", rdns.Verified)
}

Validation Methods

Validate Method

The Validate() method provides a summary of all authentication checks:

validation := email.AuthResults.Validate()

fmt.Printf("Passed: %v\n", validation.Passed)
fmt.Printf("SPF Passed: %v\n", validation.SPFPassed)
fmt.Printf("DKIM Passed: %v\n", validation.DKIMPassed)
fmt.Printf("DMARC Passed: %v\n", validation.DMARCPassed)
fmt.Printf("ReverseDNS Passed: %v\n", validation.ReverseDNSPassed)
fmt.Printf("Failures: %v\n", validation.Failures)

AuthValidation Struct

type AuthValidation struct {
    Passed           bool     // True if SPF, DKIM, and DMARC all passed
    SPFPassed        bool     // SPF passed
    DKIMPassed       bool     // At least one DKIM passed
    DMARCPassed      bool     // DMARC passed
    ReverseDNSPassed bool     // Reverse DNS passed
    Failures         []string // Slice of failure descriptions
}

Validation Examples

All checks pass:

validation := email.AuthResults.Validate()

// AuthValidation{
//     Passed:           true,
//     SPFPassed:        true,
//     DKIMPassed:       true,
//     DMARCPassed:      true,
//     ReverseDNSPassed: true,
//     Failures:         [],
// }

if !validation.Passed {
    t.Error("expected all authentication checks to pass")
}

Some checks fail:

validation := email.AuthResults.Validate()

// AuthValidation{
//     Passed:           false,
//     SPFPassed:        false,
//     DKIMPassed:       true,
//     DMARCPassed:      false,
//     ReverseDNSPassed: true,
//     Failures: []string{
//         "SPF check failed: fail (domain: example.com)",
//         "DMARC policy: fail (policy: reject)",
//     },
// }

if !validation.Passed {
    fmt.Println("Authentication failures:")
    for _, failure := range validation.Failures {
        fmt.Printf("  - %s\n", failure)
    }
}

IsPassing Method

Quick check if all primary authentication checks passed:

if email.AuthResults.IsPassing() {
    fmt.Println("All authentication checks passed")
} else {
    fmt.Println("Some authentication checks failed")
}

Note: IsPassing() is equivalent to Validate().Passed and checks SPF, DKIM, and DMARC. Reverse DNS is not included in this check.

Package-Level Validation Functions

The authresults package also provides functions that return errors for validation:

import "github.com/vaultsandbox/client-go/authresults"

// Validate all checks
if err := authresults.Validate(email.AuthResults); err != nil {
    log.Printf("validation failed: %v", err)
}

// Validate individual checks
if err := authresults.ValidateSPF(email.AuthResults); err != nil {
    log.Printf("SPF failed: %v", err)
}

if err := authresults.ValidateDKIM(email.AuthResults); err != nil {
    log.Printf("DKIM failed: %v", err)
}

if err := authresults.ValidateDMARC(email.AuthResults); err != nil {
    log.Printf("DMARC failed: %v", err)
}

if err := authresults.ValidateReverseDNS(email.AuthResults); err != nil {
    log.Printf("Reverse DNS failed: %v", err)
}

Sentinel Errors

var (
    ErrSPFFailed        = errors.New("SPF check failed")
    ErrDKIMFailed       = errors.New("DKIM check failed")
    ErrDMARCFailed      = errors.New("DMARC check failed")
    ErrReverseDNSFailed = errors.New("reverse DNS check failed")
    ErrNoAuthResults    = errors.New("no authentication results available")
)

Use errors.Is to check for specific failures with individual validation functions:

if err := authresults.ValidateSPF(email.AuthResults); err != nil {
    if errors.Is(err, authresults.ErrSPFFailed) {
        fmt.Println("SPF check failed - check your SPF record")
    } else if errors.Is(err, authresults.ErrNoAuthResults) {
        fmt.Println("No SPF results available")
    }
}

ValidationError Type

The package-level Validate() function returns a *ValidationError when validation fails, which contains all individual error messages:

type ValidationError struct {
    Errors []string
}

func (e *ValidationError) Error() string // Returns errors joined with "; "

This allows you to access individual failure messages:

if err := authresults.Validate(email.AuthResults); err != nil {
    // Type assert to access individual errors
    if ve, ok := err.(*authresults.ValidationError); ok {
        for _, msg := range ve.Errors {
            fmt.Printf("- %s\n", msg)
        }
    }
}

Note: The package-level Validate() function returns *ValidationError or ErrNoAuthResults, while the individual functions (ValidateSPF, ValidateDKIM, etc.) return their respective sentinel errors.

Testing Patterns

Strict Authentication

func TestEmailPassesAllAuthenticationChecks(t *testing.T) {
    sendEmail(inbox.EmailAddress())

    email, err := inbox.WaitForEmail(ctx, vaultsandbox.WithWaitTimeout(10*time.Second))
    if err != nil {
        t.Fatal(err)
    }

    validation := email.AuthResults.Validate()

    if !validation.Passed {
        t.Errorf("expected all checks to pass, failures: %v", validation.Failures)
    }
    if !validation.SPFPassed {
        t.Error("expected SPF to pass")
    }
    if !validation.DKIMPassed {
        t.Error("expected DKIM to pass")
    }
    if !validation.DMARCPassed {
        t.Error("expected DMARC to pass")
    }
}

Lenient Authentication

func TestEmailHasValidDKIMSignature(t *testing.T) {
    sendEmail(inbox.EmailAddress())

    email, err := inbox.WaitForEmail(ctx, vaultsandbox.WithWaitTimeout(10*time.Second))
    if err != nil {
        t.Fatal(err)
    }

    // Only check DKIM (most reliable)
    if len(email.AuthResults.DKIM) == 0 {
        t.Fatal("expected DKIM results")
    }
    if email.AuthResults.DKIM[0].Result != "pass" {
        t.Errorf("expected DKIM pass, got %s", email.AuthResults.DKIM[0].Result)
    }
}

Handling Missing Authentication

func TestHandlesEmailsWithoutAuthentication(t *testing.T) {
    email, err := inbox.WaitForEmail(ctx, vaultsandbox.WithWaitTimeout(10*time.Second))
    if err != nil {
        t.Fatal(err)
    }

    // Some senders don't have SPF/DKIM configured
    validation := email.AuthResults.Validate()

    // Log results for debugging
    if !validation.Passed {
        t.Logf("Auth failures (expected for test emails): %v", validation.Failures)
    }
}

Testing Specific Checks

func TestEmailAuthentication(t *testing.T) {
    ctx := context.Background()
    inbox, err := client.CreateInbox(ctx)
    if err != nil {
        t.Fatal(err)
    }
    defer inbox.Delete(ctx)

    sendEmail(inbox.EmailAddress())

    email, err := inbox.WaitForEmail(ctx, vaultsandbox.WithWaitTimeout(10*time.Second))
    if err != nil {
        t.Fatal(err)
    }

    t.Run("SPF check", func(t *testing.T) {
        if email.AuthResults.SPF != nil {
            result := email.AuthResults.SPF.Result
            if result != "pass" && result != "neutral" && result != "softfail" {
                t.Errorf("unexpected SPF result: %s", result)
            }
        }
    })

    t.Run("DKIM check", func(t *testing.T) {
        if len(email.AuthResults.DKIM) > 0 {
            anyPassed := false
            for _, d := range email.AuthResults.DKIM {
                if d.Result == "pass" {
                    anyPassed = true
                    break
                }
            }
            if !anyPassed {
                t.Error("expected at least one DKIM signature to pass")
            }
        }
    })

    t.Run("DMARC check", func(t *testing.T) {
        if email.AuthResults.DMARC != nil {
            result := email.AuthResults.DMARC.Result
            if result != "pass" && result != "none" {
                t.Errorf("unexpected DMARC result: %s", result)
            }
        }
    })
}

Why Authentication Matters

Production Readiness

Testing authentication catches issues like:

Misconfigured SPF records - emails rejected by Gmail/Outlook
Missing DKIM signatures - reduced deliverability
DMARC failures - emails sent to spam
Reverse DNS mismatches - flagged as suspicious

Real-World Example

func TestProductionEmailConfiguration(t *testing.T) {
    app.SendWelcomeEmail(inbox.EmailAddress())

    email, err := inbox.WaitForEmail(ctx, vaultsandbox.WithWaitTimeout(10*time.Second))
    if err != nil {
        t.Fatal(err)
    }

    validation := email.AuthResults.Validate()

    // In production, these should all pass
    if !validation.Passed {
        t.Log("Email authentication issues detected:")
        for _, f := range validation.Failures {
            t.Logf("  %s", f)
        }
        t.Log("")
        t.Log("Action required:")

        if !validation.SPFPassed {
            t.Log("- Fix SPF record for your domain")
        }
        if !validation.DKIMPassed {
            t.Log("- Configure DKIM signing in your email service")
        }
        if !validation.DMARCPassed {
            t.Log("- Add/fix DMARC policy")
        }

        t.Fail()
    }
}

Troubleshooting

No Authentication Results

if email.AuthResults.SPF == nil &&
   len(email.AuthResults.DKIM) == 0 &&
   email.AuthResults.DMARC == nil {
    fmt.Println("No authentication performed")
    fmt.Println("This may happen for:")
    fmt.Println("- Emails sent from localhost/internal servers")
    fmt.Println("- Test SMTP servers without authentication")
}

All Checks Fail

validation := email.AuthResults.Validate()

if !validation.Passed {
    fmt.Printf("Authentication failed: %v\n", validation.Failures)

    // Common causes:
    // 1. No SPF record: Add "v=spf1 ip4:YOUR_IP -all" to DNS
    // 2. No DKIM: Configure your mail server to sign emails
    // 3. No DMARC: Add "v=DMARC1; p=none" to DNS
    // 4. Wrong IP: Update SPF record with correct server IP
}

Understanding Failure Reasons

validation := email.AuthResults.Validate()

for _, failure := range validation.Failures {
    switch {
    case strings.Contains(failure, "SPF"):
        fmt.Println("Fix SPF: Update DNS TXT record for your domain")
    case strings.Contains(failure, "DKIM"):
        fmt.Println("Fix DKIM: Enable DKIM signing in your email service")
    case strings.Contains(failure, "DMARC"):
        fmt.Println("Fix DMARC: Add DMARC policy to DNS")
    }
}

Next Steps

Email Authentication Guide - Testing authentication in depth
Email API Reference - Understanding email structure
Testing Patterns - Real-world testing examples
Gateway Security - Understanding the security model