refactor(notification-outbox): extract EmailAddressValidator helper, drop orphaned using

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;
+    }
+}