MediatR error: Register your handlers with the container

I have a .Net Core app where i use the .AddMediatR extension to register the assembly for my commands and handlers

In ConfigureServices in Startup.cs i have used the extension method from the official package MediatR.Extensions.Microsoft.DependencyInjection with the following parameter:

startup.cs

 services.AddBLL();

DependencyInjection.cs

public static IServiceCollection AddBLL(this IServiceCollection services)
    {
        services.AddAutoMapper(Assembly.GetExecutingAssembly());
        services.AddMediatR(Assembly.GetExecutingAssembly());
        services.AddTransient(typeof(IPipelineBehavior<,>), typeof(RequestPerformanceBehaviour<,>));
        services.AddTransient(typeof(IPipelineBehavior<,>), typeof(RequestValidationBehavior<,>));

        return services;
    }

The commandhandler class are as follow: ListEpostaHesaplariHandler.cs

public class ListEpostaHesaplariRequest : IRequest<ResultDataDto<List<ListEpostaHesaplariDto>>>
{
    public FiltreEpostaHesaplariDto Model { get; set; }
}

public class ListEpostaHesaplariHandler : IRequestHandler<ListEpostaHesaplariRequest, ResultDataDto<List<ListEpostaHesaplariDto>>>
{
    private readonly IBaseDbContext _context;
    private readonly IMapper _mapper;

    public ListEpostaHesaplariHandler(IBaseDbContext context, IMapper mapper)
    {
        _context = context;
        _mapper = mapper;
    }

    public async Task<ResultDataDto<List<ListEpostaHesaplariDto>>> Handle(ListEpostaHesaplariRequest request, CancellationToken cancellationToken)
    {
        await Task.Delay(1);

        var resultDataDto = new ResultDataDto<List<ListEpostaHesaplariDto>>() { Status = ResultStatus.Success };

        try
        {
            var foo = _context.EpostaHesaplari;

            var filtreliEpostaHesaplari = Filtre(request.Model, foo);

            var epostaHesaplariDto = _mapper.Map<List<ListEpostaHesaplariDto>>(filtreliEpostaHesaplari);

            resultDataDto.Result = epostaHesaplariDto;
        }
        catch (Exception ex)
        {
            resultDataDto.Status = ResultStatus.Error;
            resultDataDto.AddError(ex.Message);
        }

        return resultDataDto;
    }

This is the Controller I used the MediatR

BaseController.cs

  public abstract class BaseController : Controller
{
    private IMediator _mediator;
    public static int? birimIDD;
    protected IMediator Mediator
    {
        get
        {
            return _mediator ??= HttpContext.RequestServices.GetService<IMediator>();
        }
    }
}

HomeController.cs

[HttpPost]
    public async Task<IActionResult> MailGonderAsync()
    {

        FiltreEpostaHesaplariDto filtre = new FiltreEpostaHesaplariDto();
        filtre.Durum = true;
        var req = new ListEpostaHesaplariRequest() { Model = filtre };
        var response = await Mediator.Send(req);
    }

no problem so far await Mediator.Send(req); this response is coming successfully

the problem starts from here

send.cs (in class business logic layer )

public class EmailSend : IEmailSingleSender
{
    private readonly IMediator _mediator;

    public EmailSend(IMediator mediator)
    {
        _mediator = mediator ?? throw new ArgumentNullException(nameof(mediator));

    }

    public async Task Send(EmailParamsDto emailParamsDto)
    {
        try
        {
            FiltreEpostaHesaplariDto filtre = new FiltreEpostaHesaplariDto();
            filtre.Durum = true;
            var req = new ListEpostaHesaplariRequest() { Model = filtre };
            var response = await _mediator.Send(req);

            SmtpClient smtpClient = new SmtpClient();
            smtpClient.Port = _emailSetting.Port;
            smtpClient.Host = _emailSetting.Server;
            smtpClient.EnableSsl = _emailSetting.UseSsl;
            NetworkCredential networkCredential = new NetworkCredential();
            networkCredential.UserName = _emailSetting.UserName;
            networkCredential.Password = _emailSetting.Password;
            smtpClient.Credentials = networkCredential;
            MailMessage mail = new MailMessage();
            mail.IsBodyHtml = _emailSetting.IsHtml;
            mail.From = new MailAddress(_emailSetting.UserName, emailParamsDto.Subject);
            mail.To.Add(new MailAddress(emailParamsDto.Receiver));
            //mail.CC.Add(_emailSetting.AdminMail);
            mail.Body = emailParamsDto.Body;
            mail.Subject = emailParamsDto.Subject;
            mail.Priority = emailParamsDto.MailPriority;

            await smtpClient.SendMailAsync(mail);
        }
        catch (Exception ex)
        {

            throw ex;
        }
    }
}

When this line, in the Send method, executes I get the exception:

var response = await _mediator.Send(req); 

Error constructing handler for request of type MediatR.IRequestHandler2[IUC.BaseApplication.BLL.Handlers.Yonetim.EpostaHesaplariHandlers.ListEpostaHesaplariRequest,IUC.BaseApplication.COMMON.Models.ResultDataDto1[System.Collections.Generic.List`1[IUC.BaseApplication.BLL.Models.Yonetim.EpostaHesaplariDto.ListEpostaHesaplariDto]]]. Register your handlers with the container. See the samples in GitHub for examples.