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Microsoft Office365 Pop3 Authentication Failed Using OAuth2 in C#

Astotek Dev 0 Reputation points
2024-10-18T09:50:06.4166667+00:00

I am trying to connect pop3email client with token based authentication

to create token, I have registered app in azure and using below details to generate token:

endpoint : https://login.microsoftonline.com/{tenantId}/oauth2/v2.0/token

grant : client_credentials

scope : https://outlook.office365.com/.default

token is getting generated successfully but while passing that token to pop3emailclient to connect to server getting authentication failed error.

I have provided below permissions to registered app:

Office 365 Exchange Online

Mail.Read

Mail.Read.All

Mail.Read.Shared

POP.AccessAsApp

Also tried with graph api permissions:

POP.AccessAsUser.All

offline_access

email

Mail.Read

Mail.ReadBasic.All

Microsoft Exchange Online
Office Development
Office Development
Office: A suite of Microsoft productivity software that supports common business tasks, including word processing, email, presentations, and data management and analysis.Development: The process of researching, productizing, and refining new or existing technologies.
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  1. Alex Zhang-MSFT 1,915 Reputation points Microsoft Vendor
    2024-10-21T02:41:06.4466667+00:00

    Hello, @Astotek Dev,

    Welcome to the Microsoft Q&A platform!

    Based on your description, I understand that authentication fails when you use OAuth2 in C# to connect to a POP3 email client.

    In order to solve your problem, it's important to verify a few critical points:

    1.Token Format and Usage: Ensure that the token is in the correct format and that you are passing it correctly in the POP3 client. Depending on the library you are using, the method to set the token might vary.

    2.POP3 Client Library Support: Not all POP3 client libraries support OAuth2 natively. Make sure the library you are using supports OAuth2 for POP3 connections.

    3.Permissions: Verify that the permissions you have set are adequate and that they are correctly applied to the token.

    4.Correct Client ID and Secret: Verify that the client ID and secret you are using correspond to the registered application in Azure.

    5.Tenant ID: Ensure the tenant ID is correct and corresponds to your organization's Azure AD tenant.

    By performing these steps and ensuring that all the details are configured correctly, you should be able to successfully authenticate via the POP3 client using the OAuth2 token in C#. If you continue to encounter issues, it may be worth checking the logs in Azure AD for any additional insights or error messages related to the authentication process.

    If the answer is helpful please click on ACCEPT ANSWER as it could help other members of the Microsoft Q&A community who have similar questions and are looking for solutions.

    Thank you for your support and understanding.

    Best Wishes,

    Alex Zhang

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