Download Email with Background Service in VB.NET¶

Introduction¶

In an ASP/ASP.NET email application, if email download takes longer than the timeout value (in seconds) that the current asp page is allowed to run, user will get an error “ASP Timeout”. This often happens when user has a large quantity of emails to download or user downloads emails via a slow connection. By default the timeout is set to 90 seconds, it is easy to exceed this limit.

Obviously, a solution to ASP timeout is to set ASPScriptTimeout a larger value. You may click here for details. Technically the timeout problem can be solved in this way; however, some users may get frustrated and press the stop button on the browser toolbar as he waits too long.

EAGetMail POP3 Component introduces a more intelligent method to retrieve emails in background. You should download the EAGetMail Service installer and install it on your machine at first. Then you can use MailClient.GetMailsByQueue method to send the request to EAGetMail Service, the method returns to the user immediately and the EAGetMail Service performs task in background.

[VB.NET Example - Retrieve email with background service]¶

The following example codes demonstrate how to use EAGetMail POP3 component to retrieve email with background service. In order to run it correctly, please change email server, user, password, folder, file name values.

Imports System.Globalization
Imports System.Text
Imports System.IO
Imports EAGetMail 'imports EAGetMail namespace

Module Module1

    Function _generateFileName(ByVal sequence As Integer) As String
        Dim currentDateTime As DateTime = DateTime.Now
        Return String.Format("{0}-{1:000}-{2:000}.eml",
                            currentDateTime.ToString("yyyyMMddHHmmss", New CultureInfo("en-US")),
                            currentDateTime.Millisecond,
                            sequence)
    End Function

    Sub Main()

        Try
            ' Create a folder named "inbox" under current directory
            ' to save the email retrieved.
            Dim localInbox As String = String.Format("{0}\inbox", Directory.GetCurrentDirectory())

            ' If the folder is not existed, create it.
            If Not Directory.Exists(localInbox) Then
                Directory.CreateDirectory(localInbox)
            End If

            Dim oServer As New MailServer("pop3.emailarchitect.net",
                        "test@emailarchitect.net",
                        "testpassword",
                        ServerProtocol.Pop3)

            ' Enable SSL/TLS connection, most modern email server require SSL/TLS connection by default.
            oServer.SSLConnection = True
            oServer.Port = 995

            ' If your server doesn't support SSL/TLS connection, please use the following codes
            ' oServer.SSLConnection = False
            ' oServer.Port = 110


            Dim oClient As New MailClient("TryIt")

            ' Leave a copy of message on server.
            Dim leaveCopy As Boolean = True

            ' Download emails to this local folder
            Dim downloadFolder As String = localInbox

            ' Send request to EAGetMail Service, then EAGetMail Service retrieves email
            ' in background and this method returns immediately.
            oClient.GetMailsByQueue(oServer, downloadFolder, leaveCopy)

        Catch ep As Exception
            Console.WriteLine(ep.Message)
        End Try

    End Sub
End Module

Scheduled to retrieve emails¶

EAGetMail Service provides another advanced feature which allow you set a POP3/IMAP4 account in the EAGetMail Service Manager. EAGetMail Service can download emails from this account in specified time interval. If you need to process the email in the mailbox on a regular basis, you just need to create your mail process application, you don’t need to write your email download task part.

Finally you just need to set your mail account in EAGetMail Service Manager and specify your application or COMMAND, EAGetMail service will download the emails and invoke your application automatically. Please refer to Mail Pull for more detail.

I also suggest that you have a look at Parse Non-Delivery Report (NDR) using EAGetMail Service. It demonstrates how to set a schedule to check a mailbox and insert non-delivery report to SQL database.

Next Section

At next section I will introduce how to parse email in VB.NET.