diff --git a/src/SampleProject.Application/Customers/DomainServices/CustomerEmailChecker.cs b/src/SampleProject.Application/Customers/DomainServices/CustomerEmailChecker.cs
new file mode 100644
index 0000000..800c791
--- /dev/null
+++ b/src/SampleProject.Application/Customers/DomainServices/CustomerEmailChecker.cs
@@ -0,0 +1,32 @@
+using System;
+using System.Collections.Generic;
+using System.Net.Mail;
+using System.Text;
+using SampleProject.Domain.Customers;
+
+namespace SampleProject.Application.Customers.DomainServices
+{
+    class CustomerEmailChecker : ICustomerEmailChecker
+    {
+        private readonly string _customerEmail;
+
+        public CustomerEmailChecker(string customerEmail)
+        {
+            _customerEmail = customerEmail;
+        }
+
+        public bool IsValid(string customerEmail)
+        {
+            try
+            {
+                var emailAddress = new MailAddress(customerEmail);
+            }
+            catch
+            {
+                return false;
+            }
+
+            return true;
+        }
+    }
+}
diff --git a/src/SampleProject.Application/Customers/RegisterCustomer/RegisterCustomerCommandHandler.cs b/src/SampleProject.Application/Customers/RegisterCustomer/RegisterCustomerCommandHandler.cs
index 4dee03c..2bdf419 100644
--- a/src/SampleProject.Application/Customers/RegisterCustomer/RegisterCustomerCommandHandler.cs
+++ b/src/SampleProject.Application/Customers/RegisterCustomer/RegisterCustomerCommandHandler.cs
@@ -13,20 +13,29 @@ public class RegisterCustomerCommandHandler : ICommandHandler<RegisterCustomerCo
         private readonly ICustomerRepository _customerRepository;
         private readonly ICustomerUniquenessChecker _customerUniquenessChecker;
         private readonly IUnitOfWork _unitOfWork;
+        private readonly ICustomerEmailChecker _customerEmailChecker;
 
         public RegisterCustomerCommandHandler(
             ICustomerRepository customerRepository, 
-            ICustomerUniquenessChecker customerUniquenessChecker, 
+            ICustomerUniquenessChecker customerUniquenessChecker,
+            ICustomerEmailChecker customerEmailChecker,
             IUnitOfWork unitOfWork)
         {
             this._customerRepository = customerRepository;
             _customerUniquenessChecker = customerUniquenessChecker;
+            _customerEmailChecker = customerEmailChecker;
             _unitOfWork = unitOfWork;
         }
 
         public async Task<CustomerDto> Handle(RegisterCustomerCommand request, CancellationToken cancellationToken)
         {
-            var customer = Customer.CreateRegistered(request.Email, request.Name, this._customerUniquenessChecker);
+            var customer = Customer.CreateRegistered(request.Email, request.Name, this._customerUniquenessChecker, this._customerEmailChecker);
+
+            if (customer == null)
+            {
+                // What is the best way to return error to user?
+                return new CustomerDto();
+            }
 
             await this._customerRepository.AddAsync(customer);
 
diff --git a/src/SampleProject.Domain/Customers/Customer.cs b/src/SampleProject.Domain/Customers/Customer.cs
index 14bbe6e..1dfd82a 100644
--- a/src/SampleProject.Domain/Customers/Customer.cs
+++ b/src/SampleProject.Domain/Customers/Customer.cs
@@ -1,6 +1,9 @@
 using System;
 using System.Collections.Generic;
+using System.IO;
 using System.Linq;
+using System.Linq.Expressions;
+using System.Net.Mail;
 using SampleProject.Domain.Customers.Orders;
 using SampleProject.Domain.Customers.Orders.Events;
 using SampleProject.Domain.Customers.Rules;
@@ -30,9 +33,9 @@ private Customer()
         private Customer(string email, string name)
         {
             this.Id = new CustomerId(Guid.NewGuid());
-            _email = email;
-            _name = name;
-            _welcomeEmailWasSent = false;
+            SetCustomerEmail(email);
+            SetCustomerName(name);
+            SetWelcomeEmailSentStatus(false);
             _orders = new List<Order>();
 
             this.AddDomainEvent(new CustomerRegisteredEvent(this.Id));
@@ -41,10 +44,32 @@ private Customer(string email, string name)
         public static Customer CreateRegistered(
             string email, 
             string name,
-            ICustomerUniquenessChecker customerUniquenessChecker)
+            ICustomerUniquenessChecker customerUniquenessChecker,
+            ICustomerEmailChecker customerEmailChecker = null)
         {
-            CheckRule(new CustomerEmailMustBeUniqueRule(customerUniquenessChecker, email));
-
+            try
+            {
+                if (customerEmailChecker != null)
+                {
+                    CheckRule(new CustomerEmailValidRule(customerEmailChecker, email));
+                }   
+            }
+            catch (BusinessRuleValidationException ex)
+            {
+                return null;
+            }
+
+            try
+            {
+                
+                CheckRule(new CustomerEmailMustBeUniqueRule(customerUniquenessChecker, email));
+            }
+            
+            catch(BusinessRuleValidationException ex)
+            {
+                //FIXME: Maybe throw duplicate email exception? Or log the error?
+                return null;
+            }
             return new Customer(email, name);
         }
 
@@ -91,7 +116,22 @@ public void RemoveOrder(OrderId orderId)
 
         public void MarkAsWelcomedByEmail()
         {
-            this._welcomeEmailWasSent = true;
+            SetWelcomeEmailSentStatus(true);
+        }
+
+        private void SetCustomerEmail(string email)
+        {
+            _email = email;
+        }
+
+        private void SetCustomerName(string name)
+        {
+            _name = name;
+        }
+
+        private void SetWelcomeEmailSentStatus(bool wasSent)
+        {
+            _welcomeEmailWasSent = wasSent;
         }
     }
 }
\ No newline at end of file
diff --git a/src/SampleProject.Domain/Customers/ICustomerEmailChecker.cs b/src/SampleProject.Domain/Customers/ICustomerEmailChecker.cs
new file mode 100644
index 0000000..7e5d833
--- /dev/null
+++ b/src/SampleProject.Domain/Customers/ICustomerEmailChecker.cs
@@ -0,0 +1,7 @@
+namespace SampleProject.Domain.Customers
+{
+    public interface ICustomerEmailChecker
+    {
+        bool IsValid(string customerEmail);
+    }
+}
\ No newline at end of file
diff --git a/src/SampleProject.Domain/Customers/Rules/CustomerEmailValidRule.cs b/src/SampleProject.Domain/Customers/Rules/CustomerEmailValidRule.cs
new file mode 100644
index 0000000..e226a5b
--- /dev/null
+++ b/src/SampleProject.Domain/Customers/Rules/CustomerEmailValidRule.cs
@@ -0,0 +1,27 @@
+using SampleProject.Domain.SeedWork;
+
+namespace SampleProject.Domain.Customers.Rules
+{
+    internal class CustomerEmailValidRule : IBusinessRule
+    {
+        private readonly ICustomerEmailChecker _customerEmailChecker;
+
+        private readonly string _email;
+
+        public CustomerEmailValidRule(
+            ICustomerEmailChecker customerEmailChecker,
+            string email)
+        {
+            _customerEmailChecker = customerEmailChecker;
+            _email = email;
+        }
+
+        public bool IsBroken()
+        {
+            return !_customerEmailChecker.IsValid(_email);
+        }
+        
+
+        public string Message => "Customer with this email already exists.";
+    }
+}
\ No newline at end of file
diff --git a/src/SampleProject.Infrastructure/Domain/DomainModule.cs b/src/SampleProject.Infrastructure/Domain/DomainModule.cs
index 892eb4e..4b09c4f 100644
--- a/src/SampleProject.Infrastructure/Domain/DomainModule.cs
+++ b/src/SampleProject.Infrastructure/Domain/DomainModule.cs
@@ -14,6 +14,10 @@ protected override void Load(ContainerBuilder builder)
                 .As<ICustomerUniquenessChecker>()
                 .InstancePerLifetimeScope();
 
+            builder.RegisterType<ICustomerEmailChecker>()
+                .As<ICustomerEmailChecker>()
+                .InstancePerLifetimeScope();
+
             builder.RegisterType<ForeignExchange>()
                 .As<IForeignExchange>()
                 .InstancePerLifetimeScope();