(C#) Verify Email Recipients

A way to possibly determine valid/invalid email addresses. I would recommend being very careful about doing this because your IP address may be flagged as a potential spammer by the mail server (because you are probing for valid/invalid email addresses). This Chilkat functionality existed for many years, before this kind of activity became a problem. The functionality remains only because it is useful for some to test with their own SMTP servers.

Chilkat .NET Downloads Chilkat .NET Framework Chilkat for .NET Core

// This example requires the Chilkat API to have been previously unlocked.
// See Global Unlock Sample for sample code.

Chilkat.MailMan mailman = new Chilkat.MailMan();

// SMTP connection settings...
mailman.SmtpHost = "smtp.example.com";
mailman.SmtpUsername = "MY_SMTP_USERNAME";
mailman.SmtpPassword = "MY_SMTP_PASSWORD";
mailman.SmtpSsl = true;
mailman.SmtpPort = 465;

// Create a new email object
Chilkat.Email email = new Chilkat.Email();

email.Subject = "This is a test";
email.Body = "This is a test";
email.From = "myemail@example.com";
bool success = email.AddTo("person1","person1@example.com");
success = email.AddTo("person2","person2@example.com");
success = email.AddTo("person3","person3@example.com");
// The SMTP server smtp.example.com won't know anything about an email address @somewhere_else.com
success = email.AddTo("person3","person4@somewhere_else.com");
// ...

// Verify recipients.
// **** See the warning about using this API method in the description above.
// (An SMTP server only knows valid email address for its own domain.  For example,
// smtp.example.com *may* only know if person1@example.com is valid or invalid, but does
// not know anything about the validity of email addresses having other domains.)
Chilkat.StringArray badAddrs = new Chilkat.StringArray();
success = mailman.VerifyRecips(email,badAddrs);
if (success != true) {
    Debug.WriteLine(mailman.LastErrorText);
    return;
}

int i = 0;
while (i < badAddrs.Count) {
    Debug.WriteLine(badAddrs.GetString(i));
    i = i + 1;
}

Debug.WriteLine("done.");