OAuth 2.0 with Office365/Exchange IMAP/POP3/SMTP
First you need to register your application in Azure Portal.
Here’s a detailed guide how to do that:
https://docs.microsoft.com/en-us/azure/active-directory/develop/quickstart-register-app
Then you need to apply correct API permissions and grant the admin consent for your domain.
In the API permissions / Add a permission wizard, select Microsoft Graph and then Delegated permissions to find the following permission scopes listed:
- offline_access
- IMAP.AccessAsUser.All
- POP.AccessAsUser.All
- SMTP.AccessAsUser.All
Remember to grant admin consent.
Use Microsoft Authentication Library for .NET (MSAL.NET) nuget package to obtain an access token:
https://www.nuget.org/packages/Microsoft.Identity.Client/
var pcaOptions = new PublicClientApplicationOptions
{
ClientId = "Application (client) ID",
TenantId = "Directory (tenant) ID",
RedirectUri = "https://login.microsoftonline.com/common/oauth2/nativeclient"
};
var pca = PublicClientApplicationBuilder
.CreateWithApplicationOptions(pcaOptions)
.Build();
var scopes = new string[]
{
"offline_access",
"email",
"https://outlook.office.com/IMAP.AccessAsUser.All",
"https://outlook.office.com/POP.AccessAsUser.All",
"https://outlook.office.com/SMTP.AccessAsUser.All",
};
In addition, you can request for offline_access scope. When a user approves the offline_access scope, your app can receive refresh tokens from the Microsoft identity platform token endpoint. Refresh tokens are long-lived. Your app can get new access tokens as older ones expire.
Now acquire the access token and user email address:
var authResult = pca.AcquireTokenInteractive(scopes).ExecuteAsync().Result; string user = authResult.Account.Username; string accessToken = authResult.AccessToken;
Finally you can connect to IMAP/POP3/SMTP server and authenticate:
using (Imap client = new Imap())
{
client.ConnectSSL("'outlook.office365.com");
client.LoginOAUTH2(user, accessToken);
client.SelectInbox();
// ...
client.Close();
}
As this is fairly new feature for Exchange/Office365, here are some useful links:
https://stackoverflow.com/questions/29747477/imap-auth-in-office-365-using-oauth2
https://stackoverflow.com/questions/43473858/connect-to-outlook-office-365-imap-using-oauth2