greylist fixes

mailvalidate/email_address.go

@@ -201,16 +201,16 @@ func handleDeliverableResponse(resp *EmailValidation) {
 
 func handleTemporaryFailure(req *EmailValidationRequest, resp *EmailValidation) {
 	switch {
+	case isBlacklistError(resp.SmtpResponse.Description):
+		blacklisted(req, resp)
+	case isGreylistError(resp.SmtpResponse.Description):
+		greylisted(req, resp)
 	case isMailboxFullError(resp.SmtpResponse.Description):
 		handleMailboxFull(resp)
 	case isDeliveryFailure(resp.SmtpResponse.Description, resp.SmtpResponse.ErrorCode):
 		handleDeliveryFailure(resp)
-	case isGreylistError(resp.SmtpResponse.Description):
-		greylisted(req, resp)
 	case isTLSError(resp.SmtpResponse.Description):
 		handleTLSRequirement(resp)
-	case isBlacklistError(resp.SmtpResponse.Description):
-		blacklisted(req, resp)
 	}
 }
 
@@ -363,6 +363,7 @@ func isGreylistError(description string) bool {
 		"postgrey",
 		"try again in",
 		"deferred for",
+		"internal resource temporarily unavailable",
 	}
 
 	for _, keyword := range greylistKeywords {

mailvalidate/email_address_test.go

@@ -486,6 +486,28 @@ func TestMailServerHealthIntegration(t *testing.T) {
 				RetryAfter:    0, // We'll check this is greater than current time
 			},
 		},
+		{
+			name: "should handle mimecast greylisting",
+			req: &EmailValidationRequest{
+				Email:      "test@example.com",
+				FromEmail:  "sender@test.com",
+				FromDomain: "test.com",
+			},
+			resp: &EmailValidation{
+				IsDeliverable:   "unknown",
+				RetryValidation: true,
+				SmtpResponse: SmtpResponse{
+					ResponseCode: "451",
+					Description:  "Internal resource temporarily unavailable - https://community.mimecast.com/docs/DOC-1369#451",
+				},
+			},
+			expected: MailServerHealth{
+				IsGreylisted:  true,
+				IsBlacklisted: false,
+				FromEmail:     "sender@test.com",
+				RetryAfter:    0, // We'll check this is greater than current time
+			},
+		},
 		{
 			name: "should handle temporary blacklisting",
 			req: &EmailValidationRequest{