i have create one class file for send email

public class NewSendEmailTask : IPipelineTask<PurchaseOrder>
    {
        private IEmailService EmailService { get; set; }

        private CommerceConfigurationProvider CommerceConfiguration { get; set; }

        private string EmailTypeName { get; set; }

        private ILoggingService LoggingService { get; set; }

        public NewSendEmailTask(string emailTypeName, ILoggingService loggingService, IEmailService emailService, CommerceConfigurationProvider commerceConfiguration)
        {
            this.EmailTypeName = emailTypeName;
            this.LoggingService = loggingService;
            this.EmailService = emailService;
            this.CommerceConfiguration = commerceConfiguration;
        }

        /// <summary>
        /// SendEmailTask Execute
        /// </summary>
        /// <param name="purchaseOrder"></param>
        /// <returns></returns>
        public PipelineExecutionResult Execute(PurchaseOrder purchaseOrder)
        {
            OrderAddress billingAddress = purchaseOrder.GetBillingAddress();
            if (billingAddress == (OrderAddress)null || string.IsNullOrEmpty(billingAddress.EmailAddress))
            {
                return PipelineExecutionResult.Warning;
            }
            if (purchaseOrder.Discounts.Where(x => x.CampaignItemName == "B2B").Any() && (EmailTypeName == "OrderConfirmation"))
            {
                return PipelineExecutionResult.Success;
            }; // If B2B order and mail is OrderConfirmation: mail does not have to be send, so do nothing and return Success
            CustomGlobalization customGlobalization = new CustomGlobalization(this.CommerceConfiguration);
            customGlobalization.SetCulture(new CultureInfo(purchaseOrder.CultureCode ?? customGlobalization.DefaultCulture.ToString()));
            try
            {
   this.EmailService.Send((ILocalizationContext)customGlobalization, purchaseOrder.ProductCatalogGroup.EmailProfile, this.EmailTypeName, new MailAddress(billingAddress.EmailAddress), (IDictionary<string, string>)new Dictionary<string, string>()
                {
                  {
                    "orderNumber",
                    purchaseOrder.OrderNumber
                  },
                  {
                    "orderGuid",
                    purchaseOrder.OrderGuid.ToString()
                  }
                });

            }
            catch (SmtpException ex)
            {
                this.LoggingService.Log<NewSendEmailTask>((Exception)ex);
            }
            return PipelineExecutionResult.Success;
        }
    }

after this i have create configuration file for register method

<configuration>
  <components>
    <component
         id="Checkout.NewSendEmailTask"
           service="UCommerce.Pipelines.IPipelineTask`1[[UCommerce.EntitiesV2.PurchaseOrder, UCommerce]], UCommerce"
               type="ld.Businesslogic.Pipelines.Checkout.NewSendEmail.NewSendEmailTask, ld">
      <parameters>
        <EmailTypeName>OrderConfirmation</EmailTypeName>
      </parameters>
    </component>
  </components>
  <components>
    <partial-component id="Checkout">
      <parameters>
        <tasks>
          <array>
            <value insert-before="${Checkout.SendConfirmationEmail}">${Checkout.NewSendEmailTask}</value>
            <value remove="${Checkout.SendConfirmationEmail}" />
          </array>
        </tasks>
      </parameters>
    </partial-component>
  </components>
</configuration>

and also set sendgrid credentials in web.config file

<mailSettings>
      <smtp from="from email address" deliveryMethod="Network">
        <network
                defaultCredentials="false"
                host="smtp.sendgrid.net"
                port="587"
                password="sendgrid account password"
                userName="sendgrid account username/>
      </smtp>
</mailSettings>

my site hosted in aws server

so any one know how to send email after order completed.