EmailVerify for .NET

Greylisting (or graylisting) is a simple technology aimed at defending mailboxes against spam; used by many email servers, greylisting tries to defer the acceptance of an email message by some minutes by having the target mail exchanger returning a temporarily reject, in the hope that a potential spammer would not retry the transfer because of bandwidth and timing restrictions.

EmailVerify for .NET detects greylisting conditions automatically and aborts the validation process with a specific failure; it is up to the implementor to choose if retrying the validation after some time or not.

The following code mimics a possible email validation program that takes into account a possible greylisting condition:

            var engine = new VerificationEngine();

            // ...

            var result = engine.Run("alice@example.com",
                VerificationLevel.Mailbox).Result;

            switch (result.LastStatus)
            {
                case VerificationStatus.Success:
                    // The mailbox exists
                    break;

                case VerificationStatus.MailboxTemporarilyUnavailable:
                    // Possible greylisting condition, needs to queue
                    // this validation again, in a couple of minutes

                    // ...

                    break;

                // TODO: Add more cases, if needed

                default:
                    // ...
                    break;
            }