diff --git a/src/ScadaLink.NotificationOutbox/Delivery/EmailNotificationDeliveryAdapter.cs b/src/ScadaLink.NotificationOutbox/Delivery/EmailNotificationDeliveryAdapter.cs
index 8928530..7fb8946 100644
--- a/src/ScadaLink.NotificationOutbox/Delivery/EmailNotificationDeliveryAdapter.cs
+++ b/src/ScadaLink.NotificationOutbox/Delivery/EmailNotificationDeliveryAdapter.cs
@@ -91,7 +91,7 @@ public sealed class EmailNotificationDeliveryAdapter : INotificationDeliveryAdap
 
         // A malformed sender or recipient address cannot be fixed by retrying —
         // surface it as a permanent failure (mirrors NS-008).
-        var addressError = NotificationDeliveryService.ValidateAddresses(
+        var addressError = EmailAddressValidator.ValidateAddresses(
             smtpConfig.FromAddress, recipients);
         if (addressError != null)
         {
diff --git a/src/ScadaLink.NotificationService/EmailAddressValidator.cs b/src/ScadaLink.NotificationService/EmailAddressValidator.cs
new file mode 100644
index 0000000..6fb38e9
--- /dev/null
+++ b/src/ScadaLink.NotificationService/EmailAddressValidator.cs
@@ -0,0 +1,38 @@
+using MimeKit;
+using ScadaLink.Commons.Entities.Notifications;
+
+namespace ScadaLink.NotificationService;
+
+/// <summary>
+/// NS-008: Validates the sender and recipient email addresses before an SMTP
+/// delivery is attempted, so a malformed address surfaces as a clean error
+/// string rather than a <c>ParseException</c> escaping the delivery path.
+/// <para>
+/// Public so the central Notification Outbox's <c>EmailNotificationDeliveryAdapter</c>
+/// can share this exact pre-send validation rather than carry a divergent copy.
+/// </para>
+/// </summary>
+public static class EmailAddressValidator
+{
+    /// <summary>
+    /// Validates the sender and recipient email addresses, returning a
+    /// human-readable error string if any is malformed, or null if all parse.
+    /// </summary>
+    public static string? ValidateAddresses(
+        string fromAddress, IReadOnlyList<NotificationRecipient> recipients)
+    {
+        if (!MailboxAddress.TryParse(fromAddress, out _))
+        {
+            return $"Invalid sender (from) email address: '{fromAddress}'";
+        }
+
+        var invalid = recipients
+            .Where(r => !MailboxAddress.TryParse(r.EmailAddress, out _))
+            .Select(r => r.EmailAddress)
+            .ToList();
+
+        return invalid.Count > 0
+            ? $"Invalid recipient email address(es): {string.Join(", ", invalid)}"
+            : null;
+    }
+}
diff --git a/src/ScadaLink.NotificationService/NotificationDeliveryService.cs b/src/ScadaLink.NotificationService/NotificationDeliveryService.cs
index c760e97..2508641 100644
--- a/src/ScadaLink.NotificationService/NotificationDeliveryService.cs
+++ b/src/ScadaLink.NotificationService/NotificationDeliveryService.cs
@@ -1,7 +1,6 @@
 using System.Text.Json;
 using Microsoft.Extensions.Logging;
 using Microsoft.Extensions.Options;
-using MimeKit;
 using ScadaLink.Commons.Entities.Notifications;
 using ScadaLink.Commons.Interfaces.Repositories;
 using ScadaLink.Commons.Interfaces.Services;
@@ -91,7 +90,7 @@ public class NotificationDeliveryService : INotificationDeliveryService, IDispos
         // malformed address previously caused MailboxAddress.Parse to throw a
         // ParseException that escaped SendAsync unhandled; it must instead produce a
         // clean NotificationResult the calling script can handle.
-        var addressError = ValidateAddresses(smtpConfig.FromAddress, recipients);
+        var addressError = EmailAddressValidator.ValidateAddresses(smtpConfig.FromAddress, recipients);
         if (addressError != null)
         {
             _logger.LogWarning("Notification to list {List} has invalid addresses: {Reason}", listName, addressError);
@@ -225,7 +224,7 @@ public class NotificationDeliveryService : INotificationDeliveryService, IDispos
         }
 
         // NS-008: a malformed address cannot be fixed by retrying — park it.
-        var addressError = ValidateAddresses(smtpConfig.FromAddress, recipients);
+        var addressError = EmailAddressValidator.ValidateAddresses(smtpConfig.FromAddress, recipients);
         if (addressError != null)
         {
             _logger.LogError(
@@ -344,33 +343,6 @@ public class NotificationDeliveryService : INotificationDeliveryService, IDispos
         GC.SuppressFinalize(this);
     }
 
-    /// <summary>
-    /// NS-008: Validates the sender and recipient email addresses, returning a
-    /// human-readable error string if any is malformed, or null if all parse.
-    /// <para>
-    /// Public and shared: the central Notification Outbox's
-    /// <c>EmailNotificationDeliveryAdapter</c> applies the same pre-send address
-    /// validation, so both delivery paths use this single implementation.
-    /// </para>
-    /// </summary>
-    public static string? ValidateAddresses(
-        string fromAddress, IReadOnlyList<NotificationRecipient> recipients)
-    {
-        if (!MailboxAddress.TryParse(fromAddress, out _))
-        {
-            return $"Invalid sender (from) email address: '{fromAddress}'";
-        }
-
-        var invalid = recipients
-            .Where(r => !MailboxAddress.TryParse(r.EmailAddress, out _))
-            .Select(r => r.EmailAddress)
-            .ToList();
-
-        return invalid.Count > 0
-            ? $"Invalid recipient email address(es): {string.Join(", ", invalid)}"
-            : null;
-    }
-
     /// <summary>
     /// Delivers an email via SMTP. Throws on failure (transient errors and
     /// <see cref="SmtpPermanentException"/> propagate; the caller classifies them).
diff --git a/tests/ScadaLink.NotificationService.Tests/SmtpErrorClassifierTests.cs b/tests/ScadaLink.NotificationService.Tests/SmtpErrorClassifierTests.cs
index 442934d..8ffe947 100644
--- a/tests/ScadaLink.NotificationService.Tests/SmtpErrorClassifierTests.cs
+++ b/tests/ScadaLink.NotificationService.Tests/SmtpErrorClassifierTests.cs
@@ -1,7 +1,6 @@
 using System.Net.Sockets;
 using MailKit;
 using MailKit.Net.Smtp;
-using MailKit.Security;
 
 namespace ScadaLink.NotificationService.Tests;