diff --git a/docs/tests/web/smtp-mail-exception-sanitization.md b/docs/tests/web/smtp-mail-exception-sanitization.md
new file mode 100644
index 0000000..f7dcb88
--- /dev/null
+++ b/docs/tests/web/smtp-mail-exception-sanitization.md
@@ -0,0 +1,76 @@
+# Test Evidence: Sanitized production mail exception feedback
+
+- **Test type:** Web
+- **Requirement IDs:** `INT-005`, `INT-008`
+- **Scenario IDs:** `AC-INT-002` (production mail-failure boundary)
+- **Test class/method:** `com.lab.labtimesheet.feature.integration.controller.SmtpOnboardingWebIntegrationTest#failedSmtpTestRendersActionableFeedbackWithoutActivatingTheDraft`
+- **Implementation commit:** `pending`
+
+## Protected behavior
+
+Spring Mail delivery failures from the production SMTP adapter return the fixed Admin guidance instead of escaping
+the MVC request or exposing provider diagnostics. A failed probe does not mark the draft tested or enable activation.
+
+## Test method
+
+MockMvc saves a valid draft, then the test SMTP boundary throws Spring's production-shaped `MailSendException` with a
+distinctive deterministic diagnostic. The authenticated CSRF-protected request crosses the real controller and SMTP
+configuration service, and the rendered Thymeleaf response is inspected for the fixed message, raw-text absence, and
+absence of the activation action.
+
+## Hand-derived expected result
+
+The response is HTTP 200 on `smtp/form`, contains the fixed operator guidance, omits the exception diagnostic, and
+does not offer Activate SMTP because `markTested` was never reached.
+
+## RED
+
+**Command**
+
+```text
+export JAVA_HOME=/opt/homebrew/opt/openjdk@25
+export PATH="$JAVA_HOME/bin:$PATH"
+export DOCKER_HOST=unix:///Users/sechmachine/.orbstack/run/docker.sock
+./mvnw -Dtest=SmtpOnboardingWebIntegrationTest#failedSmtpTestRendersActionableFeedbackWithoutActivatingTheDraft test
+```
+
+**Observed result**
+
+```text
+Tests run: 1, Failures: 0, Errors: 1, Skipped: 0
+MailSendException escaped as ServletException with the distinctive diagnostic instead of rendering smtp/form.
+BUILD FAILURE
+PostgreSQL: 18.4
+```
+
+## GREEN
+
+**Command**
+
+```text
+./mvnw -Dtest=SmtpOnboardingWebIntegrationTest#failedSmtpTestRendersActionableFeedbackWithoutActivatingTheDraft test
+```
+
+**Observed result**
+
+```text
+Tests run: 1, Failures: 0, Errors: 0, Skipped: 0
+BUILD SUCCESS
+PostgreSQL: 18.4
+```
+
+## Affected suite
+
+**Command and result**
+
+```text
+./mvnw -Dtest=TimeConfigurationTest,BootstrapIntegrationTest,SmtpOnboardingWebIntegrationTest,AccountActivationIntegrationTest,AccountWebIntegrationTest,BootstrapOnboardingWebIntegrationTest,JavaMailSmtpProbeTest,SecurityResponseIntegrationTest test
+Tests run: 22, Failures: 0, Errors: 0, Skipped: 0
+BUILD SUCCESS
+PostgreSQL: 18.4
+```
+
+## External-test boundaries
+
+The test exercises the production Spring Mail exception type without contacting an external SMTP server. It does not
+prove live Mailpit/provider interoperability and contains no real credential or activation token.
diff --git a/src/main/java/com/lab/labtimesheet/feature/integration/controller/SmtpController.java b/src/main/java/com/lab/labtimesheet/feature/integration/controller/SmtpController.java
index 79954a5..b3fb507 100644
--- a/src/main/java/com/lab/labtimesheet/feature/integration/controller/SmtpController.java
+++ b/src/main/java/com/lab/labtimesheet/feature/integration/controller/SmtpController.java
@@ -9,6 +9,7 @@ import com.lab.labtimesheet.feature.integration.model.dto.SmtpForm;
 import com.lab.labtimesheet.feature.integration.service.SmtpConfigurationService;
 import jakarta.servlet.http.HttpSession;
 import jakarta.validation.Valid;
+import org.springframework.mail.MailException;
 import org.springframework.stereotype.Controller;
 import org.springframework.ui.Model;
 import org.springframework.validation.BindingResult;
@@ -76,7 +77,7 @@ class SmtpController {
         try {
             smtp.testDraft(action.getDraftId(), adminId(principal), principal.getName());
             return "redirect:/admin/smtp?tested";
-        } catch (IllegalArgumentException | IllegalStateException failure) {
+        } catch (IllegalArgumentException | IllegalStateException | MailException failure) {
             bindingResult.reject("smtp.test.failed", TEST_FAILURE_MESSAGE);
             return renderActionError(model, bindingResult);
         }
diff --git a/src/test/java/com/lab/labtimesheet/feature/integration/controller/SmtpOnboardingWebIntegrationTest.java b/src/test/java/com/lab/labtimesheet/feature/integration/controller/SmtpOnboardingWebIntegrationTest.java
index 8e8c115..607b318 100644
--- a/src/test/java/com/lab/labtimesheet/feature/integration/controller/SmtpOnboardingWebIntegrationTest.java
+++ b/src/test/java/com/lab/labtimesheet/feature/integration/controller/SmtpOnboardingWebIntegrationTest.java
@@ -26,6 +26,7 @@ import org.springframework.boot.webmvc.test.autoconfigure.AutoConfigureMockMvc;
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Import;
 import org.springframework.context.annotation.Primary;
+import org.springframework.mail.MailSendException;
 import org.springframework.test.annotation.DirtiesContext;
 import org.springframework.test.context.ActiveProfiles;
 import org.springframework.test.web.servlet.MockMvc;
@@ -158,7 +159,7 @@ class SmtpOnboardingWebIntegrationTest {
                 .andReturn().getResponse().getContentAsString();
         String draftId = html.replaceAll("(?s).*name=\"draftId\" value=\"([0-9]+)\".*", "$1");
         String rawDiagnostic = "AUTH rejected for smtp-secret-raw-diagnostic";
-        probe.failureMessage = rawDiagnostic;
+        probe.failure = new MailSendException(rawDiagnostic);
 
         mockMvc.perform(post("/admin/smtp/test")
                         .with(user("admin@example.com").roles("ADMIN"))
@@ -185,12 +186,12 @@ class SmtpOnboardingWebIntegrationTest {
 
     static final class RecordingProbe implements SmtpProbe {
         private final List<String> recipients = new ArrayList<>();
-        private String failureMessage;
+        private MailSendException failure;
 
         @Override
         public void send(SmtpConnection connection, String recipient, String subject, String body) {
-            if (failureMessage != null) {
-                throw new IllegalStateException(failureMessage);
+            if (failure != null) {
+                throw failure;
             }
             recipients.add(recipient);
         }