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Unable connect to the serve error when using Access Mail Services using OAuth

I read emails from an exchange online account using imap.
This worked without problem using basic authentication. Since basic authentication will be disabled by exchange online, i need to authenticate via oAuth.

I did follow the documentation on https://docs.aspose.com/email/net/access-mail-services-using-oauth/
As described in the documentation, i’ve implemented the AzureROPCTokenProvider and configured the Exchange App Registration according to the documentation from microsoft.

The implementation AzureROPCTokenProvider seems to work and i do get a token.
image.png (50.3 KB)

This code is used for loading emails via IMAP
using (ImapClient client = new ImapClient(
//When this method is called, AzureROPCTokenProvider.GetAccessToken is called first
//AzureROPCTokenProvider.GetAccessToken returns a valid token
//Then the exception “Unable connect to the serve” occurs
var lst = client.ListMessages();

The exception is “Unable connect to the server” without any further information.
Is there a way to get more useful information what exactly is not working.
Since the token can be loaded, the server seems to be available and based on the exception message it is not clear what is wrong.

Message: Unable connect to the server.
Stack Trace:    at #=z1zUrGj5sxf9uqcjTJVcVa2E7dMDr.#=zBazcka0=(IAsyncResult #=zQXkmzSo=)
   at #=z1zUrGj5sxf9uqcjTJVcVa2E7dMDr.#=zaksmQ6s=()
   at #=z_wnR4kxf0caXFBC6Gp9X7XGpTiOTg2vkkWiZUFA=.#=zFgPZw88=(#=zzdacdi9nZ_EWsncM6CvfmmlYFeXpSJT00g== #=zpgkRhnk=)
   at #=zmXwX_0NGShfKfH1ZqtD7kQ3Kx89t.#=zxJKUZtSBJVbV(Int32 #=zytvRPTU=, #=zzdacdi9nZ_EWsncM6CvfmmlYFeXpSJT00g== #=zkkiUCAA=, List`1 #=zbj3Ohq4=, Int32 #=zbK1AP4k=)
   at #=zmXwX_0NGShfKfH1ZqtD7kQ3Kx89t.#=zxJKUZtSBJVbV(Int32 #=zbK1AP4k=, #=zzdacdi9nZ_EWsncM6CvfmmlYFeXpSJT00g== #=zkkiUCAA=, #=zcmd7ccUCbZD5dS3XOwh93Os= #=zoTRekHfrrNPb, List`1 #=zbj3Ohq4=)
   at #=zmXwX_0NGShfKfH1ZqtD7kQ3Kx89t.#=zMUR_SbDdZ5go(Int32 #=zbK1AP4k=, #=zzdacdi9nZ_EWsncM6CvfmmlYFeXpSJT00g== #=zkkiUCAA=)
   at #=z1zUrGj5sxf9uqcjTJVcVa2E7dMDr.#=z$S2KR0yn2RAT()
   at #=z1zUrGj5sxf9uqcjTJVcVa2E7dMDr.#=zxCVEsC8=(AsyncCallback #=zE_F5kXw=, Object #=zW6FV2wk=)
   at Aspose.Email.Clients.Imap.ImapClient.#=zstPvzD4qxZ8L(IConnection #=zI2W9bpw=, String #=zXuPejhM=, Int64 #=z6OxiGjHloJPV, Boolean #=zs$G70cvnVz6Q, IEnumerable`1 #=zGJgsRiNqUovN, AsyncCallback #=zE_F5kXw=, Object #=zW6FV2wk=)
   at Aspose.Email.Clients.Imap.ImapClient.ListMessages()
   at PopImapOAuthAsposeDemo.Program.Main(String[] args) in C:\project\EvidenceGit\PopImapOAuthAsposeDemo\PopImapOAuthAsposeDemo\PopImapOAuthAsposeDemo\Program.cs:line 55


Please read the following detail to achieve your requirement.

How To Enable or disable modern authentication

To use modern authentication, make sure that it is enabled. Modern authentication is enabled by default in Exchange Online. For tenants created before August 1, 2017, modern authentication is turned off by default.
In the Microsoft 365 admin center at https://admin.microsoft.com, go Settings > Org Settings > Modern Authentication. In the Modern authentication flyout that appears, you can identify the protocols that no longer require Basic authentication.
For new Office 365 tenants in Azure, Basic Authentication is disabled by default for all applications. In this case, the text will be displayed in this section.

Your organization has security defaults enabled, which means modern authentication to Exchange Online is required, and basic authentication connections are blocked. You must turn off security defaults in the Azure portal before you can change any settings here.

You can enable Basic Auth support for tenant from the Azure portal (Azure Active Directory -> Properties -> Manage Security defaults -> Enable Security defaults = No ).
For more information, see the documentation on https://docs.microsoft.com/en-us/exchange/clients-and-mobile-in-exchange-online/enable-or-disable-modern-authentication-in-exchange-online

How To use modern authentication with EwsClient

To use modern authentication with EwsClient the following is required:

  1. App registration with Azure Active Directory.
  2. Adding code to get an authentication token from a token server.
  3. Using the token to authenticate.

Note: There are two types of permissions that can be used to access EWS. Choose a specific type of permission, depending on the app you are creating:

  • Delegated permissions are used by apps that have a signed-in user present. For these apps, either the user or an administrator consents to the permissions that the app requests. In other words, when you connect to the service, a dialog window will appear to enter username and password. App can never have more privileges than the signed-in user.
  • Application permissions are used by apps that run without a signed-in user present, for example, apps that run as background services or daemons. Only an administrator can consent to application permissions.

Refer to Microsoft documentation for more information: https://docs.microsoft.com/en-us/exchange/client-developer/exchange-web-services/how-to-authenticate-an-ews-application-by-using-oauth

App registration with Azure Active Directory

The registration procedure depends on the type of permission selected. To register your app, refer to the Microsoft documentation:

You can download full code example to use modern authentication with IMAP and SMTP clients.
EWSModernAuthenticationImapSmtp.zip (3.9 KB)

The full code example you provided appears to be private and I am unable to download it.


Please download the code example from here:
EWSModernAuthenticationImapSmtp.zip (3.9 KB)