EASendMail SMTP Component > Developer Center > Example Codes > Visual Basic.NET > Send Email using MX DNS lookup - Smart Host

Visual Basic.NET - Send Email using MX DNS lookup - Smart Host

In general, we send email via specified SMTP server. How does the specified SMTP server know what address this email should be sent to? The answer is... it queries MX record of recipient's domain via DNS lookup. It then forwards this email to the SMTP server queried from DNS server. If recipient's server doesn't work fine, sender's SMTP server will send a failure-delivery report to the sender telling it failed to send out the email.

How does EASendMail SMTP component work with "Send email directly"? Firstly, it queries MX record for recipient address from DNS, then sends email to recipient's email server directly. In short, if no SMTP server is specified in the code, EASendMail will send email to recipient directly. Since querying DNS server consumes CPU time and networking resource, the performance of "Send email directly" is lower than sending email with specified SMTP server. Moreover, nowadays more and more SMTP servers block email sent from dynamic IP address, so we don't recommend you to use "Direct Send Email" except you have a static IP address or you encounter problem with your ISP SMTP server.

Every recipient may have different SMTP server, if there are multiple recipients in one message and you want to send email directly, you should send the email to the recipients one by one.

To implement this feature, you just need to put nothing to SMTP server address.

The following example codes demonstrate how to send email without specified SMTP server.

Installation

Before you can use the following sample codes, you should download the EASendMail Installer and install it on your machine at first.

Add Reference of EASendMail to Visual Basic.NET Project

To use EASendMail SMTP Component in your project, the first step is "Add reference of EASendMail to your project". Please create/open your project with Visual Studio.NET, then choose menu->"Project"->"Add Reference"->".NET"->"Browse...", and choose the EASendMail{version}.dll from your disk, click "Open"->"OK", the reference of EASendMail will be added to your project, and you can start to use EASendMail to send email in your Visual Basic.NET project.

add reference in c#

Because EASendMail has separate builds for .Net Framework, please refer to the following table and choose the correct dll.

Separate builds of run-time assembly for .Net Framework 1.1, 2.0, 3.5, 4.0 and .Net Compact Framework 2.0, 3.5.

File	.NET Framework Version
EASendMail.dll	Built with .NET Framework 1.1 It requires .NET Framework 1.1, 2.0, 3.5 or later version.
EASendMail20.dll	Built with .NET Framework 2.0 It requires .NET Framework 2.0, 3.5 or later version.
EASendMail35.dll	Built with .NET Framework 3.5 It requires .NET Framework 3.5 or later version.
EASendMaill40.dll	Built with .NET Framework 4.0 It requires .NET Framework 4.0 or later version.
EASendMailCF20.dll	Built with .NET Compact Framework 2.0 It requires .NET Compact Framework 2.0, 3.5 or later version.
EASendMailCF35.dll	Built with .NET Compact Framework 3.5 It requires .NET Compact Framework 3.5 or later version.

' The following example codes demonstrate sending email message using MX DNS lookup
' To get full sample projects, please download and install EASendMail on your machine.
' To run it correctly, please change SMTP server, user, password, sender, recipient value to yours

' Add EASendMail namespace
Imports EASendMail

Module Module1
    Sub Main()
        Dim oMail As New SmtpMail("TryIt")
        Dim oSmtp As New SmtpClient()

        ' Set sender email address, please change it to yours
        oMail.From = "test@emailarchitect.net"

        ' Set recipient email address, please change it to yours
        oMail.To = "support@emailarchitect.net"

        ' Set email subject
        oMail.Subject = "test email from VB.NET project"

        ' Set email body
        oMail.TextBody = "this is a test email sent from VB.NET project, do not reply"

        ' Do not set SMTP server address
        Dim oServer As New SmtpServer("")

        Try

            Console.WriteLine("start to send email ...")
            oSmtp.SendMail(oServer, oMail)
            Console.WriteLine("email was sent successfully!")

        Catch ep As Exception

            Console.WriteLine("failed to send email with the following error:")
            Console.WriteLine(ep.Message)
        End Try

    End Sub
End Module

Comments

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Remarks
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Visual Basic.NET - Send Email using MX DNS lookup - Smart Host

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