diff --git a/src/ScadaLink.Commons/Messages/Notification/NotificationMessages.cs b/src/ScadaLink.Commons/Messages/Notification/NotificationMessages.cs
new file mode 100644
index 0000000..d5652ea
--- /dev/null
+++ b/src/ScadaLink.Commons/Messages/Notification/NotificationMessages.cs
@@ -0,0 +1,42 @@
+namespace ScadaLink.Commons.Messages.Notification;
+
+/// <summary>
+/// Site -> Central: submit a notification for central delivery.
+/// Fire-and-forget with ack; the site retries until a <see cref="NotificationSubmitAck"/> is received.
+/// </summary>
+public record NotificationSubmit(
+    string NotificationId,
+    string ListName,
+    string Subject,
+    string Body,
+    string SourceSiteId,
+    string? SourceInstanceId,
+    string? SourceScript,
+    DateTimeOffset SiteEnqueuedAt);
+
+/// <summary>
+/// Central -> Site: ack sent after the notification row is persisted.
+/// Idempotent — safe to re-send for the same <see cref="NotificationId"/>.
+/// </summary>
+public record NotificationSubmitAck(
+    string NotificationId,
+    bool Accepted,
+    string? Error);
+
+/// <summary>
+/// Site -> Central: query the central delivery status for a <see cref="NotificationId"/>.
+/// </summary>
+public record NotificationStatusQuery(
+    string CorrelationId,
+    string NotificationId);
+
+/// <summary>
+/// Central -> Site: response carrying the current delivery status for a queried notification.
+/// </summary>
+public record NotificationStatusResponse(
+    string CorrelationId,
+    bool Found,
+    string Status,
+    int RetryCount,
+    string? LastError,
+    DateTimeOffset? DeliveredAt);
diff --git a/src/ScadaLink.Commons/Messages/Notification/NotificationOutboxQueries.cs b/src/ScadaLink.Commons/Messages/Notification/NotificationOutboxQueries.cs
new file mode 100644
index 0000000..9bb7c4d
--- /dev/null
+++ b/src/ScadaLink.Commons/Messages/Notification/NotificationOutboxQueries.cs
@@ -0,0 +1,92 @@
+namespace ScadaLink.Commons.Messages.Notification;
+
+/// <summary>
+/// Outbox UI -> Central: paginated, filtered query over the notification outbox.
+/// All filter fields are optional; <see cref="StuckOnly"/> restricts results to stuck notifications.
+/// </summary>
+public record NotificationOutboxQueryRequest(
+    string CorrelationId,
+    string? StatusFilter,
+    string? TypeFilter,
+    string? SourceSiteFilter,
+    string? ListNameFilter,
+    bool StuckOnly,
+    string? SubjectKeyword,
+    DateTimeOffset? From,
+    DateTimeOffset? To,
+    int PageNumber,
+    int PageSize);
+
+/// <summary>
+/// A single notification row summarised for outbox UI display.
+/// </summary>
+public record NotificationSummary(
+    string NotificationId,
+    string Type,
+    string ListName,
+    string Subject,
+    string Status,
+    int RetryCount,
+    string? LastError,
+    string SourceSiteId,
+    string? SourceInstanceId,
+    DateTimeOffset CreatedAt,
+    DateTimeOffset? DeliveredAt,
+    bool IsStuck);
+
+/// <summary>
+/// Central -> Outbox UI: paginated response for a <see cref="NotificationOutboxQueryRequest"/>.
+/// </summary>
+public record NotificationOutboxQueryResponse(
+    string CorrelationId,
+    bool Success,
+    string? ErrorMessage,
+    IReadOnlyList<NotificationSummary> Notifications,
+    int TotalCount);
+
+/// <summary>
+/// Outbox UI -> Central: request to immediately retry delivery of a notification.
+/// </summary>
+public record RetryNotificationRequest(
+    string CorrelationId,
+    string NotificationId);
+
+/// <summary>
+/// Central -> Outbox UI: result of a <see cref="RetryNotificationRequest"/>.
+/// </summary>
+public record RetryNotificationResponse(
+    string CorrelationId,
+    bool Success,
+    string? ErrorMessage);
+
+/// <summary>
+/// Outbox UI -> Central: request to discard (cancel) a pending or stuck notification.
+/// </summary>
+public record DiscardNotificationRequest(
+    string CorrelationId,
+    string NotificationId);
+
+/// <summary>
+/// Central -> Outbox UI: result of a <see cref="DiscardNotificationRequest"/>.
+/// </summary>
+public record DiscardNotificationResponse(
+    string CorrelationId,
+    bool Success,
+    string? ErrorMessage);
+
+/// <summary>
+/// Outbox UI -> Central: request for the notification outbox KPI summary.
+/// </summary>
+public record NotificationKpiRequest(
+    string CorrelationId);
+
+/// <summary>
+/// Central -> Outbox UI: KPI summary for the notification outbox dashboard.
+/// </summary>
+public record NotificationKpiResponse(
+    string CorrelationId,
+    int QueueDepth,
+    int StuckCount,
+    int ParkedCount,
+    int DeliveredLastInterval,
+    TimeSpan? OldestPendingAge);
diff --git a/tests/ScadaLink.Commons.Tests/Messages/NotificationMessagesTests.cs b/tests/ScadaLink.Commons.Tests/Messages/NotificationMessagesTests.cs
new file mode 100644
index 0000000..0fba09e
--- /dev/null
+++ b/tests/ScadaLink.Commons.Tests/Messages/NotificationMessagesTests.cs
@@ -0,0 +1,188 @@
+using ScadaLink.Commons.Messages.Notification;
+
+namespace ScadaLink.Commons.Tests.Messages;
+
+/// <summary>
+/// Notification Outbox: construction and value-equality tests for the
+/// site/central notification message contracts and the outbox UI query/action contracts.
+/// </summary>
+public class NotificationMessagesTests
+{
+    // ── Task 7: site/central notification message contracts ──
+
+    [Fact]
+    public void NotificationSubmit_PositionalConstruction_SetsAllFields()
+    {
+        var enqueuedAt = DateTimeOffset.UtcNow;
+        var msg = new NotificationSubmit(
+            "notif-1", "Operators", "Tank overflow", "Tank 3 has overflowed.",
+            "site-01", "inst-7", "OnAlarm", enqueuedAt);
+
+        Assert.Equal("notif-1", msg.NotificationId);
+        Assert.Equal("Operators", msg.ListName);
+        Assert.Equal("Tank overflow", msg.Subject);
+        Assert.Equal("Tank 3 has overflowed.", msg.Body);
+        Assert.Equal("site-01", msg.SourceSiteId);
+        Assert.Equal("inst-7", msg.SourceInstanceId);
+        Assert.Equal("OnAlarm", msg.SourceScript);
+        Assert.Equal(enqueuedAt, msg.SiteEnqueuedAt);
+    }
+
+    [Fact]
+    public void NotificationSubmit_AllowsNullOptionalSourceFields()
+    {
+        var msg = new NotificationSubmit(
+            "notif-2", "Operators", "Subject", "Body",
+            "site-01", null, null, DateTimeOffset.UtcNow);
+
+        Assert.Null(msg.SourceInstanceId);
+        Assert.Null(msg.SourceScript);
+    }
+
+    [Fact]
+    public void NotificationSubmit_ValueEquality_EqualWhenAllFieldsMatch()
+    {
+        var enqueuedAt = DateTimeOffset.UtcNow;
+        var a = new NotificationSubmit("n", "L", "S", "B", "site", "inst", "scr", enqueuedAt);
+        var b = new NotificationSubmit("n", "L", "S", "B", "site", "inst", "scr", enqueuedAt);
+
+        Assert.Equal(a, b);
+        Assert.Equal(a.GetHashCode(), b.GetHashCode());
+    }
+
+    [Fact]
+    public void NotificationSubmitAck_WithExpression_ChangesSingleField()
+    {
+        var ack = new NotificationSubmitAck("notif-1", true, null);
+        var rejected = ack with { Accepted = false, Error = "duplicate" };
+
+        Assert.True(ack.Accepted);
+        Assert.False(rejected.Accepted);
+        Assert.Equal("duplicate", rejected.Error);
+        Assert.Equal("notif-1", rejected.NotificationId);
+        Assert.NotEqual(ack, rejected);
+    }
+
+    [Fact]
+    public void NotificationStatusQuery_PositionalConstruction_SetsAllFields()
+    {
+        var msg = new NotificationStatusQuery("corr-1", "notif-9");
+
+        Assert.Equal("corr-1", msg.CorrelationId);
+        Assert.Equal("notif-9", msg.NotificationId);
+    }
+
+    [Fact]
+    public void NotificationStatusResponse_PositionalConstruction_SetsAllFields()
+    {
+        var deliveredAt = DateTimeOffset.UtcNow;
+        var msg = new NotificationStatusResponse(
+            "corr-1", true, "Delivered", 2, null, deliveredAt);
+
+        Assert.Equal("corr-1", msg.CorrelationId);
+        Assert.True(msg.Found);
+        Assert.Equal("Delivered", msg.Status);
+        Assert.Equal(2, msg.RetryCount);
+        Assert.Null(msg.LastError);
+        Assert.Equal(deliveredAt, msg.DeliveredAt);
+    }
+
+    // ── Task 8: outbox UI query/action contracts ──
+
+    [Fact]
+    public void NotificationOutboxQueryRequest_PositionalConstruction_SetsAllFields()
+    {
+        var from = DateTimeOffset.UtcNow.AddDays(-1);
+        var to = DateTimeOffset.UtcNow;
+        var msg = new NotificationOutboxQueryRequest(
+            "corr-1", "Stuck", "Email", "site-01", "Operators", true, "overflow",
+            from, to, 2, 50);
+
+        Assert.Equal("corr-1", msg.CorrelationId);
+        Assert.Equal("Stuck", msg.StatusFilter);
+        Assert.Equal("Email", msg.TypeFilter);
+        Assert.Equal("site-01", msg.SourceSiteFilter);
+        Assert.Equal("Operators", msg.ListNameFilter);
+        Assert.True(msg.StuckOnly);
+        Assert.Equal("overflow", msg.SubjectKeyword);
+        Assert.Equal(from, msg.From);
+        Assert.Equal(to, msg.To);
+        Assert.Equal(2, msg.PageNumber);
+        Assert.Equal(50, msg.PageSize);
+    }
+
+    [Fact]
+    public void NotificationSummary_ValueEquality_EqualWhenAllFieldsMatch()
+    {
+        var createdAt = DateTimeOffset.UtcNow;
+        var a = new NotificationSummary(
+            "n", "Email", "Ops", "S", "Pending", 1, null, "site-01", "inst-1",
+            createdAt, null, false);
+        var b = new NotificationSummary(
+            "n", "Email", "Ops", "S", "Pending", 1, null, "site-01", "inst-1",
+            createdAt, null, false);
+
+        Assert.Equal(a, b);
+        Assert.Equal(a.GetHashCode(), b.GetHashCode());
+    }
+
+    [Fact]
+    public void NotificationOutboxQueryResponse_PositionalConstruction_SetsAllFields()
+    {
+        var summary = new NotificationSummary(
+            "n", "Email", "Ops", "S", "Delivered", 0, null, "site-01", null,
+            DateTimeOffset.UtcNow, DateTimeOffset.UtcNow, false);
+        var msg = new NotificationOutboxQueryResponse(
+            "corr-1", true, null, new[] { summary }, 1);
+
+        Assert.Equal("corr-1", msg.CorrelationId);
+        Assert.True(msg.Success);
+        Assert.Null(msg.ErrorMessage);
+        Assert.Single(msg.Notifications);
+        Assert.Equal(1, msg.TotalCount);
+    }
+
+    [Fact]
+    public void RetryNotificationRequestAndResponse_RoundTripFields()
+    {
+        var request = new RetryNotificationRequest("corr-1", "notif-1");
+        var response = new RetryNotificationResponse("corr-1", true, null);
+
+        Assert.Equal("corr-1", request.CorrelationId);
+        Assert.Equal("notif-1", request.NotificationId);
+        Assert.True(response.Success);
+        Assert.Null(response.ErrorMessage);
+    }
+
+    [Fact]
+    public void DiscardNotificationRequestAndResponse_RoundTripFields()
+    {
+        var request = new DiscardNotificationRequest("corr-1", "notif-1");
+        var response = new DiscardNotificationResponse("corr-1", false, "not found");
+
+        Assert.Equal("notif-1", request.NotificationId);
+        Assert.False(response.Success);
+        Assert.Equal("not found", response.ErrorMessage);
+    }
+
+    [Fact]
+    public void NotificationKpiResponse_WithExpression_ChangesSingleField()
+    {
+        var kpi = new NotificationKpiResponse(
+            "corr-1", 10, 2, 1, 5, TimeSpan.FromMinutes(3));
+        var updated = kpi with { QueueDepth = 12 };
+
+        Assert.Equal(10, kpi.QueueDepth);
+        Assert.Equal(12, updated.QueueDepth);
+        Assert.Equal(2, updated.StuckCount);
+        Assert.Equal(TimeSpan.FromMinutes(3), updated.OldestPendingAge);
+        Assert.NotEqual(kpi, updated);
+    }
+
+    [Fact]
+    public void NotificationKpiRequest_PositionalConstruction_SetsCorrelationId()
+    {
+        var msg = new NotificationKpiRequest("corr-1");
+        Assert.Equal("corr-1", msg.CorrelationId);
+    }
+}