diff --git a/src/ScadaLink.NotificationOutbox/Delivery/EmailNotificationDeliveryAdapter.cs b/src/ScadaLink.NotificationOutbox/Delivery/EmailNotificationDeliveryAdapter.cs
new file mode 100644
index 0000000..d65d978
--- /dev/null
+++ b/src/ScadaLink.NotificationOutbox/Delivery/EmailNotificationDeliveryAdapter.cs
@@ -0,0 +1,328 @@
+using System.Net.Sockets;
+using MailKit;
+using MailKit.Net.Smtp;
+using Microsoft.Extensions.Logging;
+using Microsoft.Extensions.Options;
+using MimeKit;
+using ScadaLink.Commons.Entities.Notifications;
+using ScadaLink.Commons.Interfaces.Repositories;
+using ScadaLink.Commons.Types.Enums;
+using ScadaLink.NotificationService;
+
+namespace ScadaLink.NotificationOutbox.Delivery;
+
+/// <summary>
+/// Task 12: Email channel delivery adapter for the central notification outbox.
+///
+/// Reuses the <see cref="ScadaLink.NotificationService"/> SMTP machinery —
+/// <see cref="ISmtpClientWrapper"/>, <see cref="SmtpTlsModeParser"/>,
+/// <see cref="OAuth2TokenService"/> and the typed <see cref="SmtpPermanentException"/>.
+/// The connect/auth/send/disconnect sequence and error classification mirror
+/// <c>NotificationDeliveryService.DeliverAsync</c>; this adapter, however, maps the
+/// result to the outbox's three-way <see cref="DeliveryOutcome"/> (Success / Permanent
+/// / Transient) rather than the S&amp;F-coupled <c>NotificationResult</c>, which cannot
+/// distinguish a permanent failure from a buffered transient one.
+/// </summary>
+public sealed class EmailNotificationDeliveryAdapter : INotificationDeliveryAdapter
+{
+    private readonly INotificationRepository _repository;
+    private readonly Func<ISmtpClientWrapper> _smtpClientFactory;
+    private readonly OAuth2TokenService? _tokenService;
+    private readonly ILogger<EmailNotificationDeliveryAdapter> _logger;
+    private readonly NotificationOptions _options;
+
+    public EmailNotificationDeliveryAdapter(
+        INotificationRepository repository,
+        Func<ISmtpClientWrapper> smtpClientFactory,
+        ILogger<EmailNotificationDeliveryAdapter> logger,
+        OAuth2TokenService? tokenService = null,
+        IOptions<NotificationOptions>? options = null)
+    {
+        _repository = repository;
+        _smtpClientFactory = smtpClientFactory;
+        _logger = logger;
+        _tokenService = tokenService;
+        // Mirrors NotificationDeliveryService: NotificationOptions supplies the
+        // documented fallback values used when a deployed SmtpConfiguration row
+        // leaves a field unset (non-positive).
+        _options = options?.Value ?? new NotificationOptions();
+    }
+
+    /// <inheritdoc />
+    public NotificationType Type => NotificationType.Email;
+
+    /// <inheritdoc />
+    public async Task<DeliveryOutcome> DeliverAsync(
+        Notification notification, CancellationToken cancellationToken = default)
+    {
+        ArgumentNullException.ThrowIfNull(notification);
+
+        var list = await _repository.GetListByNameAsync(notification.ListName, cancellationToken);
+        if (list == null)
+        {
+            return DeliveryOutcome.Permanent(
+                $"notification list '{notification.ListName}' not found");
+        }
+
+        var recipients = await _repository.GetRecipientsByListIdAsync(list.Id, cancellationToken);
+        if (recipients.Count == 0)
+        {
+            return DeliveryOutcome.Permanent(
+                $"notification list '{notification.ListName}' has no recipients");
+        }
+
+        var smtpConfigs = await _repository.GetAllSmtpConfigurationsAsync(cancellationToken);
+        var smtpConfig = smtpConfigs.FirstOrDefault();
+        if (smtpConfig == null)
+        {
+            return DeliveryOutcome.Permanent("no SMTP configuration available");
+        }
+
+        // An unknown TLS mode is a configuration error that retrying cannot fix —
+        // surface it as a permanent failure (mirrors NS-005 in NotificationDeliveryService).
+        SmtpTlsMode tlsMode;
+        try
+        {
+            tlsMode = SmtpTlsModeParser.Parse(smtpConfig.TlsMode);
+        }
+        catch (ArgumentException ex)
+        {
+            _logger.LogError(
+                "Email notification to list '{List}' has an invalid SMTP TLS mode: {Reason}",
+                notification.ListName, ex.Message);
+            return DeliveryOutcome.Permanent(ex.Message);
+        }
+
+        // A malformed sender or recipient address cannot be fixed by retrying —
+        // surface it as a permanent failure (mirrors NS-008).
+        var addressError = ValidateAddresses(smtpConfig.FromAddress, recipients);
+        if (addressError != null)
+        {
+            _logger.LogWarning(
+                "Email notification to list '{List}' has invalid addresses: {Reason}",
+                notification.ListName, addressError);
+            return DeliveryOutcome.Permanent(addressError);
+        }
+
+        var recipientAddresses = recipients.Select(r => r.EmailAddress).ToList();
+
+        try
+        {
+            await SendAsync(smtpConfig, tlsMode, recipientAddresses,
+                notification.Subject, notification.Body, cancellationToken);
+
+            return DeliveryOutcome.Success(string.Join(", ", recipientAddresses));
+        }
+        catch (SmtpPermanentException ex)
+        {
+            // Permanent SMTP failure (5xx) — not retried.
+            var detail = ScrubCredentials(ex.Message, smtpConfig.Credentials);
+            _logger.LogError(
+                "Permanent SMTP failure delivering email to list '{List}': {Detail}",
+                notification.ListName, detail);
+            return DeliveryOutcome.Permanent(detail);
+        }
+        catch (OperationCanceledException) when (cancellationToken.IsCancellationRequested)
+        {
+            // A caller-requested cancellation propagates; it is neither a success
+            // nor a delivery failure.
+            throw;
+        }
+        catch (Exception ex) when (IsTransientSmtpError(ex, cancellationToken))
+        {
+            // Transient SMTP failure (4xx, socket/protocol/timeout) — eligible for retry.
+            var detail = ScrubCredentials(ex.Message, smtpConfig.Credentials);
+            _logger.LogWarning(
+                "Transient SMTP failure delivering email to list '{List}' ({ExceptionType}): {Detail}",
+                notification.ListName, ex.GetType().Name, detail);
+            return DeliveryOutcome.Transient(detail);
+        }
+        catch (Exception ex)
+        {
+            // An unclassified failure — chiefly an OAuth2 token-fetch failure. The
+            // outbox treats it as permanent: retrying a broken credential burns
+            // token-endpoint calls. (Mirrors the NS-015 default-to-permanent stance.)
+            var detail = ScrubCredentials(ex.Message, smtpConfig.Credentials);
+            _logger.LogError(
+                "Unclassified failure delivering email to list '{List}' ({ExceptionType}): {Detail}",
+                notification.ListName, ex.GetType().Name, detail);
+            return DeliveryOutcome.Permanent($"email delivery failed: {detail}");
+        }
+    }
+
+    /// <summary>
+    /// Delivers the plain-text BCC email via SMTP. Mirrors the connect/auth/send/
+    /// disconnect sequence of <c>NotificationDeliveryService.DeliverAsync</c>: a
+    /// permanent failure surfaces as <see cref="SmtpPermanentException"/>; transient
+    /// failures propagate for the caller's classifier; the connection is always torn
+    /// down in the finally block.
+    /// </summary>
+    private async Task SendAsync(
+        SmtpConfiguration config,
+        SmtpTlsMode tlsMode,
+        IReadOnlyList<string> bccAddresses,
+        string subject,
+        string body,
+        CancellationToken cancellationToken)
+    {
+        // Create exactly one client and dispose the one actually used (NS-004).
+        var smtp = _smtpClientFactory();
+        using var disposable = smtp as IDisposable;
+
+        try
+        {
+            var timeoutSeconds = config.ConnectionTimeoutSeconds > 0
+                ? config.ConnectionTimeoutSeconds
+                : _options.ConnectionTimeoutSeconds;
+            await smtp.ConnectAsync(
+                config.Host, config.Port, tlsMode, timeoutSeconds, cancellationToken);
+
+            // Resolve credentials (OAuth2 token fetched/cached by the token service).
+            var credentials = config.Credentials;
+            if (config.AuthType.Equals("oauth2", StringComparison.OrdinalIgnoreCase)
+                && _tokenService != null && credentials != null)
+            {
+                credentials = await _tokenService.GetTokenAsync(credentials, cancellationToken);
+            }
+
+            await smtp.AuthenticateAsync(config.AuthType, credentials, cancellationToken);
+            await smtp.SendAsync(config.FromAddress, bccAddresses, subject, body, cancellationToken);
+        }
+        catch (OperationCanceledException) when (cancellationToken.IsCancellationRequested)
+        {
+            // A deliberate cancellation must propagate, not be misclassified as transient.
+            throw;
+        }
+        catch (Exception ex) when (ClassifySmtpError(ex, cancellationToken) == SmtpErrorClass.Permanent
+                                   && ex is not SmtpPermanentException)
+        {
+            // Permanent SMTP failure (5xx) — surface a typed permanent exception.
+            throw new SmtpPermanentException(ex.Message, ex);
+        }
+        // Transient and SmtpPermanentException propagate unchanged for DeliverAsync's
+        // catch filters to classify.
+        finally
+        {
+            // Always tear the connection down, regardless of outcome (NS-010).
+            // Disconnect is best-effort: a disconnect failure must not mask the
+            // original delivery exception.
+            try
+            {
+                await smtp.DisconnectAsync(cancellationToken);
+            }
+            catch (Exception disconnectEx)
+            {
+                _logger.LogDebug(
+                    "Ignoring SMTP disconnect failure during cleanup: {Reason}", disconnectEx.Message);
+            }
+        }
+    }
+
+    /// <summary>
+    /// Validates the sender and recipient email addresses, returning a human-readable
+    /// error string if any is malformed, or null if all parse (mirrors NS-008).
+    /// </summary>
+    private 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;
+    }
+
+    private enum SmtpErrorClass
+    {
+        /// <summary>Cancellation or an unrecognised exception — caller decides.</summary>
+        Unknown,
+        /// <summary>Retryable failure (4xx, connection/socket/protocol error, timeout).</summary>
+        Transient,
+        /// <summary>Non-retryable failure (5xx) — must not be retried.</summary>
+        Permanent,
+    }
+
+    /// <summary>
+    /// Classifies an SMTP failure using MailKit's typed exceptions and the numeric
+    /// <see cref="SmtpStatusCode"/> rather than locale-dependent substring matching
+    /// (mirrors NS-002/NS-003 in <c>NotificationDeliveryService</c>).
+    /// </summary>
+    private static SmtpErrorClass ClassifySmtpError(Exception ex, CancellationToken cancellationToken)
+    {
+        if (ex is OperationCanceledException && cancellationToken.IsCancellationRequested)
+        {
+            return SmtpErrorClass.Unknown;
+        }
+
+        if (ex is SmtpCommandException command)
+        {
+            var code = (int)command.StatusCode;
+            if (code >= 400 && code < 500)
+            {
+                return SmtpErrorClass.Transient;
+            }
+
+            if (code >= 500 && code < 600)
+            {
+                return SmtpErrorClass.Permanent;
+            }
+
+            return SmtpErrorClass.Unknown;
+        }
+
+        if (ex is SmtpProtocolException
+            or ServiceNotConnectedException
+            or SocketException
+            or TimeoutException)
+        {
+            return SmtpErrorClass.Transient;
+        }
+
+        return SmtpErrorClass.Unknown;
+    }
+
+    private static bool IsTransientSmtpError(Exception ex, CancellationToken cancellationToken)
+    {
+        return ClassifySmtpError(ex, cancellationToken) == SmtpErrorClass.Transient;
+    }
+
+    /// <summary>
+    /// Masks SMTP credential secrets out of free text (typically an SMTP server's
+    /// exception message) before it is logged or stored. Mirrors
+    /// <c>NotificationService.CredentialRedactor</c>, which is internal to that
+    /// project and so cannot be referenced here.
+    /// </summary>
+    private static string ScrubCredentials(string? text, string? credentials)
+    {
+        if (string.IsNullOrEmpty(text) || string.IsNullOrEmpty(credentials))
+        {
+            return text ?? string.Empty;
+        }
+
+        var result = text;
+
+        // Mask each colon-delimited component (user, password, tenant, clientId,
+        // clientSecret) and the whole packed string. Longest first so a component
+        // that is a substring of another is still fully masked.
+        var parts = credentials.Split(':')
+            .Where(p => p.Length >= 4)
+            .Append(credentials)
+            .Distinct()
+            .OrderByDescending(p => p.Length);
+
+        foreach (var part in parts)
+        {
+            result = result.Replace(part, "***REDACTED***", StringComparison.Ordinal);
+        }
+
+        return result;
+    }
+}
diff --git a/src/ScadaLink.NotificationOutbox/ScadaLink.NotificationOutbox.csproj b/src/ScadaLink.NotificationOutbox/ScadaLink.NotificationOutbox.csproj
index 656ae01..64b6b1b 100644
--- a/src/ScadaLink.NotificationOutbox/ScadaLink.NotificationOutbox.csproj
+++ b/src/ScadaLink.NotificationOutbox/ScadaLink.NotificationOutbox.csproj
@@ -14,6 +14,10 @@
 
   <ItemGroup>
     <ProjectReference Include="../ScadaLink.Commons/ScadaLink.Commons.csproj" />
+    <!-- Email delivery adapter reuses the NotificationService SMTP machinery
+         (ISmtpClientWrapper, SmtpPermanentException, SmtpTlsModeParser,
+         OAuth2TokenService). -->
+    <ProjectReference Include="../ScadaLink.NotificationService/ScadaLink.NotificationService.csproj" />
   </ItemGroup>
 
   <ItemGroup>
diff --git a/tests/ScadaLink.NotificationOutbox.Tests/Delivery/EmailNotificationDeliveryAdapterTests.cs b/tests/ScadaLink.NotificationOutbox.Tests/Delivery/EmailNotificationDeliveryAdapterTests.cs
new file mode 100644
index 0000000..2f6a2e3
--- /dev/null
+++ b/tests/ScadaLink.NotificationOutbox.Tests/Delivery/EmailNotificationDeliveryAdapterTests.cs
@@ -0,0 +1,191 @@
+using System.Net.Sockets;
+using MailKit;
+using MailKit.Net.Smtp;
+using Microsoft.Extensions.Logging.Abstractions;
+using NSubstitute;
+using NSubstitute.ExceptionExtensions;
+using ScadaLink.Commons.Entities.Notifications;
+using ScadaLink.Commons.Interfaces.Repositories;
+using ScadaLink.Commons.Types.Enums;
+using ScadaLink.NotificationOutbox.Delivery;
+using ScadaLink.NotificationService;
+
+namespace ScadaLink.NotificationOutbox.Tests.Delivery;
+
+/// <summary>
+/// Task 12: Tests for the Email outbox delivery adapter — list/recipient/SMTP-config
+/// resolution, SMTP send, and the three-way (Success / Permanent / Transient) outcome
+/// classification.
+/// </summary>
+public class EmailNotificationDeliveryAdapterTests
+{
+    private readonly INotificationRepository _repository = Substitute.For<INotificationRepository>();
+    private readonly ISmtpClientWrapper _smtpClient = Substitute.For<ISmtpClientWrapper>();
+
+    private EmailNotificationDeliveryAdapter CreateAdapter()
+    {
+        return new EmailNotificationDeliveryAdapter(
+            _repository,
+            () => _smtpClient,
+            NullLogger<EmailNotificationDeliveryAdapter>.Instance);
+    }
+
+    private static Notification MakeNotification(string listName = "ops-team")
+    {
+        return new Notification(
+            Guid.NewGuid().ToString(),
+            NotificationType.Email,
+            listName,
+            "Subject",
+            "Body",
+            "site-1");
+    }
+
+    private void SetupHappyPath()
+    {
+        var list = new NotificationList("ops-team") { Id = 1 };
+        var recipients = new List<NotificationRecipient>
+        {
+            new("Alice", "alice@example.com") { Id = 1, NotificationListId = 1 },
+            new("Bob", "bob@example.com") { Id = 2, NotificationListId = 1 }
+        };
+        var smtpConfig = new SmtpConfiguration("smtp.example.com", "basic", "noreply@example.com")
+        {
+            Id = 1, Port = 587, Credentials = "user:pass", TlsMode = "starttls"
+        };
+
+        _repository.GetListByNameAsync("ops-team").Returns(list);
+        _repository.GetRecipientsByListIdAsync(1).Returns(recipients);
+        _repository.GetAllSmtpConfigurationsAsync().Returns(new List<SmtpConfiguration> { smtpConfig });
+    }
+
+    [Fact]
+    public void Type_IsEmail()
+    {
+        Assert.Equal(NotificationType.Email, CreateAdapter().Type);
+    }
+
+    [Fact]
+    public async Task Deliver_HappyPath_ReturnsSuccessWithResolvedTargets()
+    {
+        SetupHappyPath();
+        var adapter = CreateAdapter();
+
+        var outcome = await adapter.DeliverAsync(MakeNotification());
+
+        Assert.Equal(DeliveryResult.Success, outcome.Result);
+        Assert.NotNull(outcome.ResolvedTargets);
+        Assert.Contains("alice@example.com", outcome.ResolvedTargets);
+        Assert.Contains("bob@example.com", outcome.ResolvedTargets);
+        Assert.Null(outcome.Error);
+    }
+
+    [Fact]
+    public async Task Deliver_ListNotFound_ReturnsPermanent()
+    {
+        _repository.GetListByNameAsync("missing").Returns((NotificationList?)null);
+        var adapter = CreateAdapter();
+
+        var outcome = await adapter.DeliverAsync(MakeNotification("missing"));
+
+        Assert.Equal(DeliveryResult.PermanentFailure, outcome.Result);
+        Assert.Contains("missing", outcome.Error);
+        Assert.Contains("not found", outcome.Error);
+    }
+
+    [Fact]
+    public async Task Deliver_NoRecipients_ReturnsPermanent()
+    {
+        var list = new NotificationList("ops-team") { Id = 1 };
+        _repository.GetListByNameAsync("ops-team").Returns(list);
+        _repository.GetRecipientsByListIdAsync(1).Returns(new List<NotificationRecipient>());
+        var adapter = CreateAdapter();
+
+        var outcome = await adapter.DeliverAsync(MakeNotification());
+
+        Assert.Equal(DeliveryResult.PermanentFailure, outcome.Result);
+        Assert.Contains("recipient", outcome.Error);
+    }
+
+    [Fact]
+    public async Task Deliver_NoSmtpConfig_ReturnsPermanent()
+    {
+        var list = new NotificationList("ops-team") { Id = 1 };
+        _repository.GetListByNameAsync("ops-team").Returns(list);
+        _repository.GetRecipientsByListIdAsync(1).Returns(new List<NotificationRecipient>
+        {
+            new("Alice", "alice@example.com") { Id = 1, NotificationListId = 1 }
+        });
+        _repository.GetAllSmtpConfigurationsAsync().Returns(new List<SmtpConfiguration>());
+        var adapter = CreateAdapter();
+
+        var outcome = await adapter.DeliverAsync(MakeNotification());
+
+        Assert.Equal(DeliveryResult.PermanentFailure, outcome.Result);
+        Assert.Contains("SMTP", outcome.Error);
+    }
+
+    [Fact]
+    public async Task Deliver_SmtpPermanentException_ReturnsPermanent()
+    {
+        SetupHappyPath();
+        _smtpClient
+            .SendAsync(Arg.Any<string>(), Arg.Any<IEnumerable<string>>(),
+                Arg.Any<string>(), Arg.Any<string>(), Arg.Any<CancellationToken>())
+            .ThrowsAsync(new SmtpPermanentException("550 mailbox unavailable"));
+        var adapter = CreateAdapter();
+
+        var outcome = await adapter.DeliverAsync(MakeNotification());
+
+        Assert.Equal(DeliveryResult.PermanentFailure, outcome.Result);
+        Assert.Contains("mailbox unavailable", outcome.Error);
+    }
+
+    [Fact]
+    public async Task Deliver_Smtp5xxCommandException_ReturnsPermanent()
+    {
+        SetupHappyPath();
+        _smtpClient
+            .SendAsync(Arg.Any<string>(), Arg.Any<IEnumerable<string>>(),
+                Arg.Any<string>(), Arg.Any<string>(), Arg.Any<CancellationToken>())
+            .ThrowsAsync(new SmtpCommandException(
+                SmtpErrorCode.RecipientNotAccepted, SmtpStatusCode.MailboxUnavailable, "rejected"));
+        var adapter = CreateAdapter();
+
+        var outcome = await adapter.DeliverAsync(MakeNotification());
+
+        Assert.Equal(DeliveryResult.PermanentFailure, outcome.Result);
+    }
+
+    [Fact]
+    public async Task Deliver_SocketException_ReturnsTransient()
+    {
+        SetupHappyPath();
+        _smtpClient
+            .ConnectAsync(Arg.Any<string>(), Arg.Any<int>(), Arg.Any<SmtpTlsMode>(),
+                Arg.Any<int>(), Arg.Any<CancellationToken>())
+            .ThrowsAsync(new SocketException((int)SocketError.ConnectionRefused));
+        var adapter = CreateAdapter();
+
+        var outcome = await adapter.DeliverAsync(MakeNotification());
+
+        Assert.Equal(DeliveryResult.TransientFailure, outcome.Result);
+        Assert.NotNull(outcome.Error);
+    }
+
+    [Fact]
+    public async Task Deliver_Smtp4xxCommandException_ReturnsTransient()
+    {
+        SetupHappyPath();
+        _smtpClient
+            .SendAsync(Arg.Any<string>(), Arg.Any<IEnumerable<string>>(),
+                Arg.Any<string>(), Arg.Any<string>(), Arg.Any<CancellationToken>())
+            .ThrowsAsync(new SmtpCommandException(
+                SmtpErrorCode.MessageNotAccepted, SmtpStatusCode.MailboxBusy, "try later"));
+        var adapter = CreateAdapter();
+
+        var outcome = await adapter.DeliverAsync(MakeNotification());
+
+        Assert.Equal(DeliveryResult.TransientFailure, outcome.Result);
+    }
+}