Sending an Email using VB.NET and smtp.office365.com

Question

1. I am trying to write a code that sends Emails using VB.NET.

2. The SMTP Server is smtp.office365.com.

3. I found plenty of resources on how to do this using the Gmail SMTP server. It works fine. But the requirement is to send the Email from the company's Email that runs over a office365.

4. The project is a Windows Forms Application. I am using Visual Studio 2010.

5. What did I try?

I have tried this code:

Dim Mail As New MailMessage
        Dim SMTP As New SmtpClient("smtp.office365.com")
        Mail.Subject = "Test Subject"
        Mail.From = New MailAddress("The from Email")
        SMTP.Credentials = New System.Net.NetworkCredential("The from Email", "The from Email Password")
        Mail.To.Add("The to Email")
        Mail.Body = "Hello"
        SMTP.EnableSsl = True
        SMTP.Port = "587"
        ServicePointManager.ServerCertificateValidationCallback = New System.Net.Security.RemoteCertificateValidationCallback(AddressOf customCertValidation)
        Try
            SMTP.Send(Mail)
            MsgBox("done")
        Catch ex As Exception
            MsgBox(ex.ToString)
        End Try

In the same form, I have a function defined as follows:

Private Shared Function customCertValidation(ByVal sender As Object, _
                                        ByVal cert As X509Certificate, _
                                        ByVal chain As X509Chain, _
                                        ByVal errors As SslPolicyErrors) As Boolean

        Return True

End Function

By running the above code, I get this message (after around a minute): System.Net.Mail. Smtp Exception: The operation has timed out. at System.Net.Mail.SmtpClient.Send(MailMessage message)

6. Also, Here, they mentioned a similar issue. I tried to use their code which is the following:

Imports System.Net.Mail

Public Class Form1

    Private Sub SendEmail()
        Dim MS365Email As New MailMessage
        MS365Email.To.Add("RECIPIENTEMAIL")
        MS365Email.From = New MailAddress("SENDEREMAIL")
        MS365Email.Subject = "SUBJECT"
        MS365Email.IsBodyHtml = True
        MS365Email.Body = "BODYTEXT"

        Dim MS365client As New SmtpClient("smtp.office365.com", 587)
        MS365Email.Priority = MailPriority.Normal

        MS365client.EnableSsl = True
        MS365client.UseDefaultCredentials = False
        Dim xms365 As New Net.NetworkCredential("USERNAME", "PASSWORD")
        MS365client.Credentials = xms365
        MS365client.DeliveryMethod = SmtpDeliveryMethod.Network
        MS365client.SendAsync(MS365Email, Nothing)
    End Sub

End Class

It does not throw any error or exception. But no Email is received.

7. What I am Expecting? Either pointing-out the issue(s) that fix any of these codes, or sharing another code that can achieve the requirement.

Thank you in advance

Answer 1

Try using SSL/TLS enabled like the following code shows:

var Client = new SmtpClient("smtp.office365.com", 587);
Client.EnableSsl = true;
Client.Credentials = new System.Net.NetworkCredential("mail", "pass");
ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls;

You may find similar questions posted, see Send SMTP email using System.Net.Mail via Exchange Online (Office 365) and Send SMTP email testing Microsoft Office 365 in .net for more information.