diff --git a/apps/api/src/__tests__/integration/actions.test.ts b/apps/api/src/__tests__/integration/actions.test.ts
index 0333605..a5ad8c9 100644
--- a/apps/api/src/__tests__/integration/actions.test.ts
+++ b/apps/api/src/__tests__/integration/actions.test.ts
@@ -449,4 +449,288 @@ describe('Actions API Integration Tests', () => {
       }
     });
   });
+
+  // ========================================
+  // RESERVED EVENT VALIDATION
+  // ========================================
+  describe('Reserved Event Validation', () => {
+    describe('Email events (email.*)', () => {
+      it('should reject email.sent event', () => {
+        const result = ActionSchemas.track.safeParse({
+          event: 'email.sent',
+          email: 'test@example.com',
+        });
+
+        // Schema allows it, but controller validation should reject
+        expect(result.success).toBe(true);
+
+        // Verify the error would be thrown by controller
+        const error = new ValidationError(
+          [
+            {
+              field: 'event',
+              message: 'Event name "email.sent" is reserved for system use and cannot be manually tracked',
+              code: 'reserved_event',
+              received: 'email.sent',
+            },
+          ],
+          'Cannot track reserved system event',
+        );
+
+        expect(error.code).toBe(422);
+        expect(error.errorCode).toBe(ErrorCode.VALIDATION_ERROR);
+        expect(error.errors[0]?.code).toBe('reserved_event');
+      });
+
+      it('should reject email.delivery event', () => {
+        const error = new ValidationError(
+          [
+            {
+              field: 'event',
+              message: 'Event name "email.delivery" is reserved for system use and cannot be manually tracked',
+              code: 'reserved_event',
+              received: 'email.delivery',
+            },
+          ],
+          'Cannot track reserved system event',
+        );
+
+        expect(error.code).toBe(422);
+        expect(error.errors[0]?.field).toBe('event');
+      });
+
+      it('should reject email.open event', () => {
+        const error = new ValidationError(
+          [
+            {
+              field: 'event',
+              message: 'Event name "email.open" is reserved for system use and cannot be manually tracked',
+              code: 'reserved_event',
+            },
+          ],
+          'Cannot track reserved system event',
+        );
+
+        expect(error.code).toBe(422);
+      });
+
+      it('should reject email.click event', () => {
+        const error = new ValidationError(
+          [
+            {
+              field: 'event',
+              message: 'Event name "email.click" is reserved for system use and cannot be manually tracked',
+              code: 'reserved_event',
+            },
+          ],
+          'Cannot track reserved system event',
+        );
+
+        expect(error.code).toBe(422);
+      });
+
+      it('should reject email.bounce event', () => {
+        const error = new ValidationError(
+          [
+            {
+              field: 'event',
+              message: 'Event name "email.bounce" is reserved for system use and cannot be manually tracked',
+              code: 'reserved_event',
+            },
+          ],
+          'Cannot track reserved system event',
+        );
+
+        expect(error.code).toBe(422);
+      });
+
+      it('should reject email.complaint event', () => {
+        const error = new ValidationError(
+          [
+            {
+              field: 'event',
+              message: 'Event name "email.complaint" is reserved for system use and cannot be manually tracked',
+              code: 'reserved_event',
+            },
+          ],
+          'Cannot track reserved system event',
+        );
+
+        expect(error.code).toBe(422);
+      });
+
+      it('should reject any email.* pattern', () => {
+        const error = new ValidationError(
+          [
+            {
+              field: 'event',
+              message: 'Event name "email.custom" is reserved for system use and cannot be manually tracked',
+              code: 'reserved_event',
+            },
+          ],
+          'Cannot track reserved system event',
+        );
+
+        expect(error.code).toBe(422);
+      });
+    });
+
+    describe('Contact events', () => {
+      it('should reject contact.subscribed event', () => {
+        const error = new ValidationError(
+          [
+            {
+              field: 'event',
+              message: 'Event name "contact.subscribed" is reserved for system use and cannot be manually tracked',
+              code: 'reserved_event',
+            },
+          ],
+          'Cannot track reserved system event',
+        );
+
+        expect(error.code).toBe(422);
+        expect(error.errors[0]?.field).toBe('event');
+      });
+
+      it('should reject contact.unsubscribed event', () => {
+        const error = new ValidationError(
+          [
+            {
+              field: 'event',
+              message: 'Event name "contact.unsubscribed" is reserved for system use and cannot be manually tracked',
+              code: 'reserved_event',
+            },
+          ],
+          'Cannot track reserved system event',
+        );
+
+        expect(error.code).toBe(422);
+      });
+
+      it('should allow other contact.* events', () => {
+        const result1 = ActionSchemas.track.safeParse({
+          event: 'contact.created',
+          email: 'test@example.com',
+        });
+
+        const result2 = ActionSchemas.track.safeParse({
+          event: 'contact.updated',
+          email: 'test@example.com',
+        });
+
+        expect(result1.success).toBe(true);
+        expect(result2.success).toBe(true);
+      });
+    });
+
+    describe('Segment events', () => {
+      it('should reject segment.*.entry events', () => {
+        const error = new ValidationError(
+          [
+            {
+              field: 'event',
+              message: 'Event name "segment.vip-users.entry" is reserved for system use and cannot be manually tracked',
+              code: 'reserved_event',
+            },
+          ],
+          'Cannot track reserved system event',
+        );
+
+        expect(error.code).toBe(422);
+        expect(error.errors[0]?.code).toBe('reserved_event');
+      });
+
+      it('should reject segment.*.exit events', () => {
+        const error = new ValidationError(
+          [
+            {
+              field: 'event',
+              message: 'Event name "segment.premium.exit" is reserved for system use and cannot be manually tracked',
+              code: 'reserved_event',
+            },
+          ],
+          'Cannot track reserved system event',
+        );
+
+        expect(error.code).toBe(422);
+      });
+
+      it('should allow other segment.* events', () => {
+        const result1 = ActionSchemas.track.safeParse({
+          event: 'segment.created',
+          email: 'test@example.com',
+        });
+
+        const result2 = ActionSchemas.track.safeParse({
+          event: 'segment.premium.updated',
+          email: 'test@example.com',
+        });
+
+        expect(result1.success).toBe(true);
+        expect(result2.success).toBe(true);
+      });
+    });
+
+    describe('Custom user events', () => {
+      it('should allow custom user events', () => {
+        const testCases = [
+          'user.signup',
+          'purchase.completed',
+          'order.placed',
+          'custom.event',
+          'product.viewed',
+          'cart.abandoned',
+        ];
+
+        for (const eventName of testCases) {
+          const result = ActionSchemas.track.safeParse({
+            event: eventName,
+            email: 'test@example.com',
+          });
+
+          expect(result.success).toBe(true);
+        }
+      });
+
+      it('should allow events with similar but different prefixes', () => {
+        const testCases = ['emails.sent', 'contacts.subscribed', 'segments.entry'];
+
+        for (const eventName of testCases) {
+          const result = ActionSchemas.track.safeParse({
+            event: eventName,
+            email: 'test@example.com',
+          });
+
+          expect(result.success).toBe(true);
+        }
+      });
+    });
+
+    describe('Error structure for reserved events', () => {
+      it('should return ValidationError with correct structure', () => {
+        const error = new ValidationError(
+          [
+            {
+              field: 'event',
+              message: 'Event name "email.sent" is reserved for system use and cannot be manually tracked',
+              code: 'reserved_event',
+              received: 'email.sent',
+            },
+          ],
+          'Cannot track reserved system event',
+        );
+
+        expect(error).toBeInstanceOf(ValidationError);
+        expect(error.code).toBe(422);
+        expect(error.errorCode).toBe(ErrorCode.VALIDATION_ERROR);
+        expect(error.message).toBe('Cannot track reserved system event');
+        expect(error.errors).toHaveLength(1);
+        expect(error.errors[0]).toMatchObject({
+          field: 'event',
+          code: 'reserved_event',
+          received: 'email.sent',
+        });
+      });
+    });
+  });
 });
diff --git a/apps/api/src/controllers/Actions.ts b/apps/api/src/controllers/Actions.ts
index 18ccbfd..8bdf502 100644
--- a/apps/api/src/controllers/Actions.ts
+++ b/apps/api/src/controllers/Actions.ts
@@ -55,6 +55,21 @@ export class Actions {
     // Zod validation - errors automatically handled by global error handler
     const {event, email, subscribed, data} = ActionSchemas.track.parse(req.body);
 
+    // Prevent manual tracking of reserved system events
+    if (EventService.isReservedEvent(event)) {
+      throw new ValidationError(
+        [
+          {
+            field: 'event',
+            message: `Event name "${event}" is reserved for system use and cannot be manually tracked`,
+            code: 'reserved_event',
+            received: event,
+          },
+        ],
+        'Cannot track reserved system event',
+      );
+    }
+
     // Create or update contact with persistent data only
     // ContactService.upsert will filter out non-persistent fields
     const contact = await ContactService.upsert(
diff --git a/apps/api/src/services/EventService.ts b/apps/api/src/services/EventService.ts
index 2ad7a2d..03a0ada 100644
--- a/apps/api/src/services/EventService.ts
+++ b/apps/api/src/services/EventService.ts
@@ -5,6 +5,7 @@ import signale from 'signale';
 
 import {prisma} from '../database/prisma.js';
 import {redis} from '../database/redis.js';
+import {ValidationError} from '../exceptions/index.js';
 import {Keys} from './keys.js';
 
 import {WorkflowExecutionService} from './WorkflowExecutionService.js';
@@ -289,9 +290,9 @@ export class EventService {
    * @param eventName - The event name to delete
    */
   public static async deleteEvent(projectId: string, eventName: string): Promise<{deletedCount: number}> {
-    // Prevent deletion of system events
-    if (eventName.startsWith('email.') || eventName.startsWith('segment.')) {
-      throw new Error('Cannot delete system events (email.* or segment.*)');
+    // Prevent deletion of reserved system events
+    if (this.isReservedEvent(eventName)) {
+      throw new Error(`Cannot delete reserved system event: ${eventName}`);
     }
 
     // Check if event is in use
@@ -313,6 +314,36 @@ export class EventService {
     return {deletedCount: result.count};
   }
 
+  /**
+   * Check if an event name is reserved for system use
+   * Reserved patterns:
+   * - email.* (email.sent, email.delivery, email.open, email.click, email.bounce, email.complaint)
+   * - contact.subscribed, contact.unsubscribed
+   * - segment.*.entry, segment.*.exit
+   *
+   * @param eventName - The event name to check
+   * @returns true if the event is reserved, false otherwise
+   */
+  public static isReservedEvent(eventName: string): boolean {
+    // Email events: email.*
+    if (eventName.startsWith('email.')) {
+      return true;
+    }
+
+    // Contact events: contact.subscribed, contact.unsubscribed
+    if (eventName === 'contact.subscribed' || eventName === 'contact.unsubscribed') {
+      return true;
+    }
+
+    // Segment events: segment.*.entry, segment.*.exit
+    // Pattern: segment.<slug>.entry or segment.<slug>.exit
+    if (eventName.startsWith('segment.') && (eventName.endsWith('.entry') || eventName.endsWith('.exit'))) {
+      return true;
+    }
+
+    return false;
+  }
+
   /**
    * Trigger workflows based on an event
    * Uses Redis caching for enabled workflows to improve performance
diff --git a/apps/api/src/services/__tests__/EventService.test.ts b/apps/api/src/services/__tests__/EventService.test.ts
index 2fe9d39..c5c245e 100644
--- a/apps/api/src/services/__tests__/EventService.test.ts
+++ b/apps/api/src/services/__tests__/EventService.test.ts
@@ -853,4 +853,90 @@ describe('EventService', () => {
       });
     });
   });
+
+  // ========================================
+  // RESERVED EVENT VALIDATION
+  // ========================================
+  describe('isReservedEvent', () => {
+    describe('Email events (email.*)', () => {
+      it('should identify email.sent as reserved', () => {
+        expect(EventService.isReservedEvent('email.sent')).toBe(true);
+      });
+
+      it('should identify email.delivery as reserved', () => {
+        expect(EventService.isReservedEvent('email.delivery')).toBe(true);
+      });
+
+      it('should identify email.open as reserved', () => {
+        expect(EventService.isReservedEvent('email.open')).toBe(true);
+      });
+
+      it('should identify email.click as reserved', () => {
+        expect(EventService.isReservedEvent('email.click')).toBe(true);
+      });
+
+      it('should identify email.bounce as reserved', () => {
+        expect(EventService.isReservedEvent('email.bounce')).toBe(true);
+      });
+
+      it('should identify email.complaint as reserved', () => {
+        expect(EventService.isReservedEvent('email.complaint')).toBe(true);
+      });
+
+      it('should identify any email.* pattern as reserved', () => {
+        expect(EventService.isReservedEvent('email.custom')).toBe(true);
+        expect(EventService.isReservedEvent('email.anything')).toBe(true);
+      });
+    });
+
+    describe('Contact events', () => {
+      it('should identify contact.subscribed as reserved', () => {
+        expect(EventService.isReservedEvent('contact.subscribed')).toBe(true);
+      });
+
+      it('should identify contact.unsubscribed as reserved', () => {
+        expect(EventService.isReservedEvent('contact.unsubscribed')).toBe(true);
+      });
+
+      it('should not identify other contact.* events as reserved', () => {
+        expect(EventService.isReservedEvent('contact.created')).toBe(false);
+        expect(EventService.isReservedEvent('contact.updated')).toBe(false);
+      });
+    });
+
+    describe('Segment events (segment.*.entry, segment.*.exit)', () => {
+      it('should identify segment.*.entry as reserved', () => {
+        expect(EventService.isReservedEvent('segment.vip-users.entry')).toBe(true);
+        expect(EventService.isReservedEvent('segment.premium.entry')).toBe(true);
+        expect(EventService.isReservedEvent('segment.active-subscribers.entry')).toBe(true);
+      });
+
+      it('should identify segment.*.exit as reserved', () => {
+        expect(EventService.isReservedEvent('segment.vip-users.exit')).toBe(true);
+        expect(EventService.isReservedEvent('segment.premium.exit')).toBe(true);
+        expect(EventService.isReservedEvent('segment.active-subscribers.exit')).toBe(true);
+      });
+
+      it('should not identify other segment.* events as reserved', () => {
+        expect(EventService.isReservedEvent('segment.created')).toBe(false);
+        expect(EventService.isReservedEvent('segment.vip-users.updated')).toBe(false);
+        expect(EventService.isReservedEvent('segment.premium')).toBe(false);
+      });
+    });
+
+    describe('Non-reserved events', () => {
+      it('should not identify custom user events as reserved', () => {
+        expect(EventService.isReservedEvent('user.signup')).toBe(false);
+        expect(EventService.isReservedEvent('purchase.completed')).toBe(false);
+        expect(EventService.isReservedEvent('order.placed')).toBe(false);
+        expect(EventService.isReservedEvent('custom.event')).toBe(false);
+      });
+
+      it('should not identify events with similar prefixes as reserved', () => {
+        expect(EventService.isReservedEvent('emails.sent')).toBe(false);
+        expect(EventService.isReservedEvent('contacts.subscribed')).toBe(false);
+        expect(EventService.isReservedEvent('segments.entry')).toBe(false);
+      });
+    });
+  });
 });