(VB.NET) 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.

Dim mailman As 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
Dim email As New Chilkat.Email

email.Subject = "This is a test"
email.Body = "This is a test"
email.From = "myemail@example.com"
Dim success As Boolean = 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.)
Dim badAddrs As New Chilkat.StringArray
success = mailman.VerifyRecips(email,badAddrs)
If (success <> True) Then
    Debug.WriteLine(mailman.LastErrorText)
    Exit Sub
End If


Dim i As Integer = 0
While i < badAddrs.Count
    Debug.WriteLine(badAddrs.GetString(i))
    i = i + 1
End While

Debug.WriteLine("done.")