add optional dkim configuration

helpers/inbound/inbound.go

@@ -233,10 +233,37 @@ func (email *ParsedEmail) parseHeaders(headers string) {
 	}
 }
 
+// ValidateConfig adds configuration options for validating a parsed email. Specifically turning DKIM as optional. DKIM validates emails in transit from tampering. However many valid email clients
+// do not have it configured
+// SPF could potentially be added but it poses a more significant security risk
+type ValidateConfig struct {
+	dkimOptional bool
+}
+
+// NewValidateConfig returns a configuration struct for validating the parsed email. Specifically turning DKIM as optional. DKIM validates emails in transit from tampering. However many valid email clients
+// do not have it configured
+func NewValidateConfig() ValidateConfig {
+	return ValidateConfig{}
+}
+
+// WithDKIMOptional validates DKIM values only if they exist. This allows the inbound client to support more email clients that might not support this configuration
+func (vc ValidateConfig) WithDKIMOptional() ValidateConfig {
+	vc.dkimOptional = true
+	return vc
+}
+
 // Validate validates the DKIM and SPF scores to ensure that the email client and address was not spoofed
-func (email *ParsedEmail) Validate() error {
-	if len(email.rawValues["dkim"]) == 0 || len(email.rawValues["SPF"]) == 0 {
-		return fmt.Errorf("missing DKIM and SPF score")
+func (email *ParsedEmail) Validate(config ...ValidateConfig) error {
+	var dkimOptional bool
+	if len(config) > 0 {
+		dkimOptional = config[0].dkimOptional
+	}
+	if len(email.rawValues["SPF"]) == 0 {
+		return fmt.Errorf("missing SPF score")
+	}
+
+	if !dkimOptional && len(email.rawValues["dkim"]) == 0 {
+		return fmt.Errorf("missing DKIM score")
 	}
 
 	for _, val := range email.rawValues["dkim"] {

helpers/inbound/inbound_test.go

@@ -136,13 +136,18 @@ func TestValidate(t *testing.T) {
 		name          string
 		values        map[string][]string
 		expectedError error
+		config        ValidateConfig
 	}{
 		{
-			name:          "MissingHeaders",
+			name:          "MissingSPFHeaders",
 			values:        map[string][]string{},
-			expectedError: fmt.Errorf("missing DKIM and SPF score"),
+			expectedError: fmt.Errorf("missing SPF score"),
 		},
 		{
+			name:          "MissingDKIMHeaders",
+			values:        map[string][]string{"SPF": {"pass"}},
+			expectedError: fmt.Errorf("missing DKIM score"),
+		}, {
 			name:          "FailedDkim",
 			values:        map[string][]string{"dkim": {"pass", "fail", "pass"}, "SPF": {"pass"}},
 			expectedError: fmt.Errorf("DKIM validation failed"),
@@ -161,13 +166,29 @@ func TestValidate(t *testing.T) {
 			name:   "success",
 			values: map[string][]string{"dkim": {"pass", "pass", "pass"}, "SPF": {"pass", "pass", "pass"}},
 		},
+		{
+			name:   "dkimOptionalAndPresent",
+			values: map[string][]string{"dkim": {"pass", "pass", "pass"}, "SPF": {"pass", "pass", "pass"}},
+			config: NewValidateConfig().WithDKIMOptional(),
+		},
+		{
+			name:          "dkimOptionalWithFailure",
+			values:        map[string][]string{"dkim": {"fail", "pass", "pass"}, "SPF": {"pass", "pass", "pass"}},
+			config:        NewValidateConfig().WithDKIMOptional(),
+			expectedError: fmt.Errorf("DKIM validation failed"),
+		},
+		{
+			name:   "dkimOptionalAndAbsent",
+			values: map[string][]string{"SPF": {"pass", "pass", "pass"}},
+			config: NewValidateConfig().WithDKIMOptional(),
+		},
 	}
 
 	for _, test := range tests {
 		t.Run(test.name, func(subTest *testing.T) {
 			//Load POST body
 			email := ParsedEmail{rawValues: test.values}
-			err := email.Validate()
+			err := email.Validate(test.config)
 
 			if test.expectedError != nil {
 				assert.EqualError(subTest, test.expectedError, err.Error())