VBNET smtp retry send failed email address - vb.net

Question

hello fellow :) i am having a trouble on how can i retry sending failed email recipients. i am trying to make an application in vbnet where i can send emails to multiple address.
some code snippet:
Dim SmtpServer As New SmtpClient()
SmtpServer.Credentials = New Net.NetworkCredential(xInformation(0), xInformation(1))
SmtpServer.Port = CInt(xInformation(2))
SmtpServer.Host = xInformation(3)
SmtpServer.EnableSsl = True
Dim mail As New MailMessage()
mail = New MailMessage
mail.From = New MailAddress(xInformation(4), "Display Name")
mail.CC.Add(xInformation(5)) ' i will make a loop here to add recipients
mail.Subject = xInformation(6)
mail.IsBodyHtml = True
mail.Body = xInformation(7)
SmtpServer.Send(mail)
question arises:
1.) if i have to send, for instance, email to 5 recipients, and only
3 emails have been successfully sent, how can i know the
failed email addresses?
2.) where is the failed email address stored?
3.) what exceptions are needed to trapped this error?

Answer 1

I don't think you can catch these exceptions in your code, the emails that do not get sent you will want to check on the smtp server there should be a mail folder within inetpub
\\ServerName\c$\Inetpub\mailroot
Inside of this folder you should find a folder called: BadMail and Drop please look at the contents of these. Your VB code doesn't have access to what a valid email address might be, only that it will try to send an smtp email message, if it fails then the SMTP application handles that.
Per your comment:
Imports System.Net.Mail
Imports System.Threading
Imports System.Web.Configuration
''' <summary>
''' Provides a method for sending email.
''' </summary>
Public NotInheritable Class Email
Private Sub New()
End Sub
''' <summary>
''' Constructs and sends an email message.
''' </summary>
''' <param name="fromName">The display name of the person the email is from.</param>
''' <param name="fromEmail">The email address of the person the email is from.</param>
''' <param name="subject">The subject of the email.</param>
''' <param name="body">The body of the email.</param>
Public Shared Sub Send(fromName As String, fromEmail As String, subject As String, body As String)
Dim message As New MailMessage() With { _
Key .IsBodyHtml = False, _
Key .From = New MailAddress(fromEmail, fromName), _
Key .Subject = subject, _
Key .Body = body _
}
message.[To].Add(WebConfigurationManager.AppSettings("mailToAddresses"))
Dim originalRecipientCount As Integer = message.[To].Count
Dim failOnAnyAddress As Boolean = Convert.ToBoolean(WebConfigurationManager.AppSettings("failOnAnyAddress"))
Try
Send(message)
Catch generatedExceptionName As SmtpFailedRecipientException
If message.[To].Count = originalRecipientCount Then
' all recipients failed
Throw
End If
If failOnAnyAddress Then
' some (not ALL) recipients failed
Throw
End If
End Try
End Sub
Private Shared Sub Send(message As MailMessage)
Dim client As New SmtpClient()
Try
client.Send(message)
Catch ex As SmtpFailedRecipientsException
' multiple fail
message.[To].Clear()
For Each sfrEx As SmtpFailedRecipientException In ex.InnerExceptions
CheckStatusAndReaddress(message, sfrEx)
Next
If message.[To].Count > 0 Then
' wait 5 seconds, try a second time
Thread.Sleep(5000)
client.Send(message)
Else
Throw
End If
Catch ex As SmtpFailedRecipientException
' single fail
message.[To].Clear()
CheckStatusAndReaddress(message, ex)
If message.[To].Count > 0 Then
' wait 5 seconds, try a second time
Thread.Sleep(5000)
client.Send(message)
Else
Throw
End If
Finally
message.Dispose()
End Try
End Sub
Private Shared Sub CheckStatusAndReaddress(message As MailMessage, exception As SmtpFailedRecipientException)
Dim statusCode As SmtpStatusCode = exception.StatusCode
If statusCode = SmtpStatusCode.MailboxBusy OrElse statusCode = SmtpStatusCode.MailboxUnavailable OrElse statusCode = SmtpStatusCode.TransactionFailed Then
message.[To].Add(exception.FailedRecipient)
End If
End Sub
End Class
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