VB.NET/ASP.NET/ASP MVC - Send email using Microsoft OAuth 2.0 (Modern Authentication) + EWS protocol from Office 365 in background service

You can send email using traditional user/password authentication from Office 365 account by EWS Protocol.

However Microsoft will disable traditional user authentication in the future, switching to Microsoft OAuth (Modern Authentication) is strongly recommended now.


Before you can use the following codes, please download EASendMail SMTP Component and install it on your machine at first. Full sample proejcts are included in this installer.

Install from NuGet

You can also install the run-time assembly by NuGet. Run the following command in the NuGet Package Manager Console:

Install-Package EASendMail


If you install it by NuGet, no sample projects are installed, only .NET assembly is installed.

Add reference

To use EASendMail SMTP Component in your project, the first step is Add reference of EASendMail to your project. Please create or open your project with Visual Studio, then go to menu -> Project -> Add Reference -> .NET -> Browse..., and select Installation Path\Lib\net[version]\EASendMail.dll from your disk, click Open -> OK, the reference of EASendMail will be added to your project, and you can start to use it to send email in your project.

add reference in c#/vb.net/c++/cli/clr

.NET assembly

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, 4.5, 4.6.1, .NET Core 2.1 and .NET Compact Framework 2.0, 3.5.

File .NET Framework Version
Lib\net11\EASendMail.dll Built with .NET Framework 1.1
It requires .NET Framework 1.1, 2.0, 3.5 or later version.
Lib\net20\EASendMail.dll Built with .NET Framework 2.0
It requires .NET Framework 2.0, 3.5 or later version.
Lib\net35\EASendMail.dll Built with .NET Framework 3.5
It requires .NET Framework 3.5 or later version.
Lib\net40\EASendMail.dll Built with .NET Framework 4.0
It requires .NET Framework 4.0 or later version.
Lib\net45\EASendMail.dll Built with .NET Framework 4.5
It requires .NET Framework 4.5 or later version.
Lib\net461\EASendMail.dll Built with .NET Framework 4.6.1
It requires .NET Framework 4.6.1 or later version.
Lib\netcoreapp2.1\EASendMail.dll Built with .NET Core 2.1
It requires .NET Core 2.1 or later version.
Lib\net20-cf\EASendMail.dll Built with .NET Compact Framework 2.0
It requires .NET Compact Framework 2.0, 3.5 or later version.
Lib\net35-cf\EASendMail.dll Built with .NET Compact Framework 3.5
It requires .NET Compact Framework 3.5 or later version.

Office 365 OAuth 2.0 client credentials grant

Normal OAuth requires user input user/password for authentication. Obviously, it is not suitable for background service. In this case, You can use the OAuth 2.0 client credentials grant, sometimes called two-legged OAuth, to access web-hosted resources by using the identity of an application. It only works for Office365 user, it doesn’t work for personal Hotmail account.

Create your application in Azure Portal

To use Microsoft/Office365/Live OAuth (Modern Authentication) in your application, you must create a application in Azure Portal.


You can use any Microsoft user to create the application, it doesn’t require application owner is administrator in your Office365 domain. But your Office365 administrator must authorize the application to access user mailbox.

  • Sign in to the Azure portal using either a work or school account or a personal Microsoft account.
  • If your account gives you access to more than one tenant, select your account in the top right corner, and set your portal session to the Azure AD tenant that you want.
  • In the left-hand navigation pane, select the Azure Active Directory service, and then select App registrations -> New registration.
azure portal new app registration

Single tenant and multitenant in account type

When the register an application page appears, enter a meaningful application name and select the account type.

Select which accounts you would like your application to support.

  • If your application only supports the users in your directory or organization, please select Single tenant type;
  • If your application needs to support all users in Office 365 and Microsoft personal account (hotmail.com, outlook.com), please select Multitenant type, and you must verify publisher.

Because we just need to support Offic365 user in our organization, so select Accounts in this organizational directory only (single tenant).

Do not select supporting Microsoft personal account, because there is no way to access Microsoft personal account in background service.


If you don’t verify publisher for multitenant application, your application will not request access token successfully.

API permissions

  • Click API Permission -> Microsoft Graph -> Delegated Permission -> User.Read.
  • Click API Permission -> Add a permission -> APIs in my organization uses -> Office 365 Exchange Online -> Application Permission -> Other permission -> full_access_as_app
azure APIs in my organization uses

Here is permissions list:

azure application api permission list

If your current user is not a user in a verified domain or Offic 365, you will not find Office 365 Exchange Online in API list, then you have to add this API permission manually.

  • Select Manifest in the left-hand navigation under Manage.
  • Locate the requiredResourceAccess property in the manifest, and add the following inside the square brackets ([]):
  "resourceAppId": "00000002-0000-0ff1-ce00-000000000000",
  "resourceAccess": [
          "id": "dc890d15-9560-4a4c-9b7f-a736ec74ec40",
          "type": "Role"
  • Select Save.
  • Select API permissions under Manage. Confirm that the full_access_as_app permission is listed.

Client Id and client secrets

Now we need to create a client secret for the application, click Certificates and secrets -> client secrets and add a new client secret.

azure application api permission

After client secret is created, store the client secret value to somewhere.


Please store client secret value by yourself, because it is hidden when you view it at next time.

Branding and verify publisher

Now we click Branding, you can edit your company logo, URL and application name. If your application supports multitenant (access user in all Office 365 and Microsoft personal account), you must complete the publisher verification.

It is not difficult, you can have a look at publisher verification. After publisher verification is completed, your branding is like this:

azure application Authentication Overview


You must complete the publisher verification for multitenant application, otherwise, your application will not request access token correctly.

Client id and tenant

Now you can click Overview to find your client id and tenant.

azure application client id and tenant

Access token expiration

You don’t have to request access token every time. By default, access token expiration time is 3600 seconds, you can use the access token repeatedly before it is expired.


You should create your client id and client secret, do not use the client id from example codes in production environment, it is used for test purpose. If you got "This app isn't verified" information, please click "Advanced" -> Go to ... for test.

VB.NET/ASP.NET/ASP MVC - Send email using Microsoft OAuth 2.0 from Office 365 account in background service - example

Imports  System
Imports  System.Text
Imports  System.Net
Imports  EASendMail

Private Shared Function _postString(ByVal uri As String, ByVal requestData As String) As String
    Dim httpRequest As HttpWebRequest = TryCast(WebRequest.Create(uri), HttpWebRequest)
    httpRequest.Method = "POST"
    httpRequest.ContentType = "application/x-www-form-urlencoded"

    Using requestStream As Stream = httpRequest.GetRequestStream()
        Dim requestBuffer As Byte() = Encoding.UTF8.GetBytes(requestData)
        requestStream.Write(requestBuffer, 0, requestBuffer.Length)
    End Using

        Dim httpResponse As HttpWebResponse = TryCast(httpRequest.GetResponse(), HttpWebResponse)
        Using reader As New StreamReader(httpResponse.GetResponseStream())
            Dim responseText = reader.ReadToEnd()
            Return responseText
        End Using

    Catch ex As WebException

        If ex.Status = WebExceptionStatus.ProtocolError Then
            Dim response = TryCast(ex.Response, HttpWebResponse)
            If response IsNot Nothing Then
                Console.WriteLine("HTTP: " & response.StatusCode)
                ' reads response body
                Using reader As StreamReader = New StreamReader(response.GetResponseStream())
                    Dim responseText As String = reader.ReadToEnd()
                End Using
            End If
        End If

        Throw ex
    End Try

End Function

Public Sub SendMail()
        Dim client_id As String = "8f54719b-4070-41ae-91ad-f48e3c793c5f"
        Dim client_secret As String = "cbmYyGQjz[d29wL2ArcgoO7HLwJXL/-."

        ' If your application is not created by Office365 administrator,
        ' please use Office365 directory tenant id, you should ask Offic365 administrator to send it to you.
        ' Office365 administrator can query tenant id in https://portal.azure.com/ - Azure Active Directory.
        Dim tenant As String = "79a42c6f-5a9a-439b-a2ca-7aa1b0ed9776"

        Dim requestData As String = String.Format("client_id={0}&client_secret={1}&scope=https://outlook.office365.com/.default&grant_type=client_credentials",
                            client_id, client_secret)

        Dim tokenUri As String = String.Format("https://login.microsoftonline.com/{0}/oauth2/v2.0/token", tenant)

        Dim responseText As String = _postString(tokenUri, requestData)
        Dim parser As OAuthResponseParser = New OAuthResponseParser()

        Dim officeUser As String = "user@mydomain.onmicrosoft.com"

        Dim server = New SmtpServer("outlook.office365.com")
        server.Protocol = ServerProtocol.ExchangeEWS

        server.User = officeUser
        server.Password = parser.AccessToken

        server.AuthType = SmtpAuthType.XOAUTH2
        server.ConnectType = SmtpConnectType.ConnectSSLAuto

        Dim mail = New SmtpMail("TryIt")
        mail.From = officeUser
        mail.[To] = "support@emailarchitect.net"
        mail.Subject = "Office 365 background service oauth test"
        mail.TextBody = "this is a test, do not reply"

        Dim smtp = New SmtpClient()
        smtp.SendMail(server, mail)
        Console.WriteLine("Message delivered!")

    Catch ep As Exception
    End Try
End Sub

TLS 1.2 protocol

TLS is the successor of SSL, more and more SMTP servers require TLS 1.2 encryption now.

If your operating system is Windows XP/Vista/Windows 7/Windows 2003/2008/2008 R2/2012/2012 R2, you need to enable TLS 1.2 protocol in your operating system like this:

Enable TLS 1.2 on Windows XP/Vista/7/10/Windows 2008/2008 R2/2012



If you have any comments or questions about above example codes, please click here to add your comments.