DeliveryStatusNotification.Failure for invalid recipient address

[nilankadharmadasa]

Hi,

I use Mailkit SmtpClient and I have the following overridden method in my code.

    protected override DeliveryStatusNotification? GetDeliveryStatusNotifications(MimeMessage message, MailboxAddress mailbox)
    {
        if(_receipt_options.TryRemove(message.MessageId, out var receitpt_option) && receitpt_option == Contracts.Data.ReceiptOptions.DeliveryReceipt)
        {
            return DeliveryStatusNotification.Success | DeliveryStatusNotification.Failure | DeliveryStatusNotification.Delay;
        }
        return DeliveryStatusNotification.Failure;
    }

I get the delivery success notifications in sender's inbox as expected.
I want to test if DeliveryStatusNotification.Failure works as expected. I tried sending emails to invalid addresses and I didn't receive any delivery failure notifications in sender's inbox. Is there anything else I need to do to receive delivery failure notifications with Mailkit?

We used System.Net.Mail before and with that, I receive delivery failure notifications for invalid addresses.

[jstedfast]

There shouldn't be anything else as far as I know.

Feel free to read up on the spec here: https://datatracker.ietf.org/doc/html/rfc3461