public class EmailAccessor : IEmailAccessor
{
    private string senderEmail;
    private string senderUsername;
    private string senderPassword;
    private int port;

    public EmailAccessor(string senderEmail, string senderUsername, string senderPassword, int port)
    {
        this.senderEmail = senderEmail;
        this.senderUsername = senderUsername;
        this.senderPassword = senderPassword;
        this.port = port;
    }
    //...
}

public class NotificationEngine : INotificationEngine
{
    private IEmailAccessor emailAccessor;

    public NotificationEngine(IEmailAccessor emailAccessor)
    {
        this.emailAccessor = emailAccessor;
    }
    //...
}

[RoutePrefix("api/email")]
public class EmailController : ApiController
{
    private INotificationEngine notificationEngine;

    public EmailController(INotificationEngine notificationEngine)
    {
        this.notificationEngine = notificationEngine;
    }

    [HttpPost]
    [Route("send")]
    public void Post([FromBody] EmailNotification email)
    {
        //...
    }
    //...
}

public static class UnityConfig
{
    public static void RegisterTypes(IUnityContainer container)
    {
        container.LoadConfiguration();

        //...

        container.RegisterType<IEmailAccessor, EmailAccessor>(new InjectionConstructor(
                ConfigurationManager.AppSettings["SenderEmail"],
                ConfigurationManager.AppSettings["SenderUsername"],
                ConfigurationManager.AppSettings["SenderPassword"],
                int.Parse(ConfigurationManager.AppSettings["Port"])));
        container.RegisterType<INotificationEngine, NotificationEngine>();

        DependencyResolver.SetResolver(new UnityDependencyResolver(container));

    }
}

{
    "Message": "No HTTP resource was found that matches the request URI 'http://localhost:63855/api/email/send'.",
    "MessageDetail": "No type was found that matches the controller named 'email'."
}