For some time it was possible to re-enable Basic Auth for IMAP and POP3 for your tenant –
– it is no longer possible to do that anymore.

You can find more details here:
https://techcommunity.microsoft.com/t5/exchange-team-blog/basic-authentication-deprecation-in-exchange-online-time-s-up/ba-p/3695312

Switch to OAuth 2.0

You should switch to OAuth 2.0 for authentication purposes:

Daemons/Services: Password grant (MFA/2FA must be turned off for this account):
https://www.limilabs.com/blog/oauth2-password-grant-office365-exchange-imap-pop3-smtp

Daemons/Services: Client credential flow:
https://www.limilabs.com/blog/oauth2-client-credential-flow-office365-exchange-imap-pop3-smtp

Web apps (requires user interaction):
https://www.limilabs.com/blog/oauth2-web-flow-office365-exchange-imap-pop3-smtp

Standalone devices (requires very little interaction):
https://www.limilabs.com/blog/oauth2-device-flow-office365-exchange-imap-pop3-smtp

Desktop apps (requires user interaction):
https://www.limilabs.com/blog/oauth2-office365-exchange-imap-pop3-smtp

Below steps are deprecated

If you want to opt-out, read the article below:

https://techcommunity.microsoft.com/t5/exchange-team-blog/basic-authentication-and-exchange-online-september-2021-update/ba-p/2772210

…or you can go directly to the self-help diagnostic (use your tenant’s Global Admin account):

https://aka.ms/PillarEXOBasicAuth

It’ll bring up the diagnostic in the Microsoft 365 admin center (if you’re a tenant Global Admin).

Hit Run Tests:

….on the next screen you’ll be able to enable Basic Auth for IMAP or POP3:

For accounts that use shared infrastructure you’ll need to run those 2 powershell commands:

Connect-ExchangeOnline
Enable-OrganizationCustomization

The post Office 365: Prevent Basic Auth being disabled first appeared on Blog | Limilabs.

• OAuth 2.0 with Office365/Exchange IMAP/POP3/SMTP
• OAuth 2.0 web flow with Office365/Exchange IMAP/POP3/SMTP
• OAuth 2.0 password grant with Office365/Exchange IMAP/POP3/SMTP
• OAuth 2.0 device flow with Office365/Exchange IMAP/POP3/SMTP
• OAuth 2.0 client credential flow with Office365/Exchange IMAP/POP3/SMTP

This article shows how to implement OAuth 2.0 client credential flow to access Office365 via IMAP, POP3 using Mail.dll .net email client. This flow is particularly useful for daemon/service apps that need to monitor certain mailboxes, without any user interaction.

Make sure IMAP/POP3 is enabled for your organization and mailbox:
Enable IMAP/POP3/SMTP in Office 365

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

Add permissions to your application in the API permissions / Add a permission wizard:

Select APIs my organization uses and search for “Office 365 Exchange Online“:

…then click Application permissions:

For POP access, choose the POP.AccessAsApp permission.
For IMAP access, choose the IMAP.AccessAsApp permission.
For SMTP access, choose the SMTP.SendAsApp permission.

Remember to Grant admin consent:

Create an application secret in Certificates & secrets panel by clicking ‘New client secret’ button:

Note the secret value as it is shown only during creation.

Use Windows PowerShell on your machine to Register service principals in Exchange.

Set execution policy first:

Set-ExecutionPolicy RemoteSigned

Install ExchangeOnlineManagement module:

Install-Module -Name ExchangeOnlineManagement 
Import-Module ExchangeOnlineManagement 

Connect and log-in as an administrator (you’ll be prompted for password):

Connect-ExchangeOnline
 -UserPrincipalName your-admin-account@your-domain.onmicrosoft.com

For Exchange running in hybrid mode log-in using following code:

$lc = Get-Credential
Connect-ExchangeOnline -Credential $lc

Create service principal

New-ServicePrincipal
 -AppId <APPLICATION_ID>
 -ServiceId <OBJECT_ID> 
 [-Organization <ORGANIZATION_ID>]

You can find ApplicationId and ObjectId in Enterprise applications in your application’s Overview panel:

Make sure you use the Object ID from the Enterprise Application. 

Do not use the value from the App Registration screen. 

In our case:

New-ServicePrincipal
 -AppId 061851f7-08c0-40bf-99c1-ebd489c11f16
 -ServiceId 4352fc11-5c2f-4b0b-af40-447ff10664e8

Note: If you still get an error running the New-ServicePrincipal cmdlet after you perform these steps, it is likely due to the fact that the user doesn’t have enough permissions in Exchange online to perform the operation. By default this cmdlet is available to users assigned the Role Management role

Add permissions to a specific mailbox:

Add-MailboxPermission
 -Identity "<USER@your-domain.onmicrosoft.com>"
 -User <OBJECT_ID>
 -AccessRights FullAccess

In our case:

Add-MailboxPermission
 -Identity "AdeleV@your-domain.onmicrosoft.com"
 -User 4352fc11-5c2f-4b0b-af40-447ff10664e8
 -AccessRights FullAccess

Shared mailboxes

You need to use Add-MailboxPermission for every shared mailbox you need access to:

Add-MailboxPermission
 -Identity "shared@your-domain.onmicrosoft.com"
 -User <OBJECT_ID>
 -AccessRights FullAccess

Let’s code

Use Microsoft Authentication Library for .NET (MSAL.NET) nuget package to obtain an access token:
https://www.nuget.org/packages/Microsoft.Identity.Client/

// C#

string clientId = "Application (client) ID";    // 061851f7-...
string tenantId = "Directory (tenant) ID";
string clientSecret = "Client secret value";

string userName = "Username/email for mailbox";    // AdeleV@...

var app = ConfidentialClientApplicationBuilder
    .Create(clientId)
    .WithTenantId(tenantId)
    .WithClientSecret(clientSecret)
    .Build();

string[] scopes = new string[] { 
    "https://outlook.office365.com/.default" 
};

' VB.NET

Dim clientId As String = "Application (client) ID" ' 061851f7-...
Dim tenantId As String = "Directory (tenant) ID"
Dim clientSecret As String = "Client secret value"

Dim userName As String = "Username/email for mailbox"  'AdeleV@...

Dim app = ConfidentialClientApplicationBuilder.Create(clientId) _
    .WithTenantId(tenantId) _
    .WithClientSecret(clientSecret) _
    .Build()

Dim scopes As String() = New String() { _
    "https://outlook.office365.com/.default" _
}

Now acquire an access token:

// C#

var result = await app.AcquireTokenForClient(scopes)
    .ExecuteAsync();

string accessToken = result.AccessToken;

' VB.NET

Dim result = Await app.AcquireTokenForClient(scopes).ExecuteAsync()
Dim accessToken As String = result.AccessToken

Finally you can connect using IMAP/POP3, authenticate and download user’s emails:

// C#

using (Imap client = new Imap())
{
    client.ConnectSSL("outlook.office365.com");
    client.LoginOAUTH2(userName, accessToken);
 
    client.SelectInbox();

    List<long> uids = imap.Search(Flag.Unseen);
    foreach (long uid in uids)
    {
        IMail email = new MailBuilder()
                .CreateFromEml(imap.GetMessageByUID(uid));
        string subject = email.Subject;
   }

   client.Close();
} 

' VB.NET

Using client As Imap = New Imap()
    client.ConnectSSL("outlook.office365.com")
    client.LoginOAUTH2(userName, accessToken)

    client.SelectInbox()

    Dim uids As List(Of Long) = imap.Search(Flag.Unseen)
    For Each uid As Long In uids
        Dim email As IMail = New MailBuilder() _
            .CreateFromEml(imap.GetMessageByUID(uid))
        Dim subject As String = email.Subject
    Next

    client.Close()
End Using

SMTP

Microsoft started supporting client credential flow and SMTP recently.

SMTP requires SMTP.SendAsApp permission added to your AD application.

All other OAuth flows (web, desktop, password grant, device) support SMTP client access as well.

For SMTP non-OAuth2 access:

“SMTP AUTH will still be available when Basic authentication is permanently disabled on October 1, 2022.” (https://docs.microsoft.com/en-us/exchange/clients-and-mobile-in-exchange-online/deprecation-of-basic-authentication-exchange-online)

However Microsoft disables SMTP AUTH in all tenants in which it’s not being used.

Here’s how to enable SMTP AUTH:
https://learn.microsoft.com/en-us/exchange/clients-and-mobile-in-exchange-online/authenticated-client-smtp-submission

Additionally Exchange Online will permanently remove support for Basic authentication with SMTP submission in September 2025:
https://techcommunity.microsoft.com/blog/exchange/exchange-online-to-retire-basic-auth-for-client-submission-smtp-auth/4114750

Troubleshooting

1. Start with PowerShell commands:

Get-ServicePrincipal
Get-MailboxPermission -Identity "AdeleV@your-domain.onmicrosoft.com"

You should see following results:

Make sure the ServiceId is the same as the Object ID on the Enterprise Application screen (do not use the value from the App Registration screen)

Make sure the AppId is the same as the Application ID on the Enterprise Application screen

2. Check if you can connect to this account using IMAP and regular interactive flow:

https://www.limilabs.com/blog/office-365-oauth-2-0-imap-pop3-email-client-connectivity-tools

This proves you have IMAP access properly configured.

3. Check if you added correct permissions and have granted Admin consent for your domain.

4. Usually people use incorrect client/tenant ids/secrets – double check every single value you enter (also for additional spaces).

5. You may need to wait 20-30 minutes for some changes to take effect (it really may take this long!).

Additional links

https://docs.microsoft.com/en-us/powershell/exchange/exchange-online-powershell-v2?view=exchange-ps#install-and-maintain-the-exo-v2-module
https://docs.microsoft.com/en-us/exchange/client-developer/legacy-protocols/how-to-authenticate-an-imap-pop-smtp-application-by-using-oauth#use-client-credentials-grant-flow-to-authenticate-imap-and-pop-connections

The post OAuth 2.0 client credential flow with Office365/Exchange IMAP/POP3/SMTP first appeared on Blog | Limilabs.

• OAuth 2.0 with Office365/Exchange IMAP/POP3/SMTP
• OAuth 2.0 web flow with Office365/Exchange IMAP/POP3/SMTP
• OAuth 2.0 password grant with Office365/Exchange IMAP/POP3/SMTP
• OAuth 2.0 device flow with Office365/Exchange IMAP/POP3/SMTP
• OAuth 2.0 client credential flow with Office365/Exchange IMAP/POP3/SMTP

This article shows how to implement OAuth 2.0 web flow to access Office365 via IMAP, POP3 or SMTP using Mail.dll .net email client.

Make sure IMAP/POP3/SMTP is enabled for your organization and mailbox:
Enable IMAP/POP3/SMTP in Office 365

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

RedirectUri

Add an authentication redirect uri to your application:

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
• email
• IMAP.AccessAsUser.All
• POP.AccessAsUser.All
• SMTP.Send

Remember to Grant admin consent:

Create an app secret and remember its value:

Use Microsoft Authentication Library for .NET (MSAL.NET) nuget package to obtain an access token:
https://www.nuget.org/packages/Microsoft.Identity.Client/

string clientId = "Application (client) ID";
string tenantId = "Directory (tenant) ID";
string clientSecret = "Client secret value";

// for @outlook.com/@hotmail accounts instead of setting .WithTenantId use:
// .WithAuthority(AadAuthorityAudience.PersonalMicrosoftAccount)

var app = ConfidentialClientApplicationBuilder
    .Create(clientId)
    .WithTenantId(tenantId)
    .WithClientSecret(clientSecret)
    .WithRedirectUri("http://localhost/myapp/")
    .Build();
// This allows saving access/refresh tokens to some storage
TokenCacheHelper.EnableSerialization(app.UserTokenCache);

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.Send",
};

In addition, you should request 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 try finding account by an identifier (it will be null on first access) in MSAL cache:

string userName;
string accessToken;

string identifier = null;

var account = await app.GetAccountAsync(identifier);

try
{
    AuthenticationResult refresh = await app
        .AcquireTokenSilent(scopes, account)
        .WithForceRefresh(true)
        .ExecuteAsync();

    userName = refresh.Account.Username;
    accessToken = refresh.AccessToken;

}
catch (MsalUiRequiredException e)
{
    // no token cache entry - perform authentication:

    Uri msUri = await app
        .GetAuthorizationRequestUrl(scopes)
        .ExecuteAsync();

    // Add a redirect code to the above 
    // Microsoft authentication uri and end this request.
}

On the first run user will be redirected to the msUri and will see a Microsoft login screen, with option to log-in, using a known account and granting access to the app (if needed):

After successful authentication Microsoft will redirect user’s browser back to your application – to the app’s RedirectUri (in our case http://localhost/MyApp/):

http://localhost/myapp/?code=0.Aa…AA&client_info=ey…I0In0&session_state=4dd….4488c8#

Controller responsible for handling this request should retrieve code parameter

string code = "get from url after redirect";

AuthenticationResult result = await app
    .AcquireTokenByAuthorizationCode(scopes, code)
    .ExecuteAsync();

string identifier = result.Account.HomeAccountId.Identifier;
string userName = result.Account.Username;
string accessToken = result.AccessToken;

Finally you can connect using IMAP/POP3/SMTP, authenticate and download user’s emails:

using (Imap client = new Imap())
{
    client.ConnectSSL("outlook.office365.com");
    client.LoginOAUTH2(userName, accessToken);
 
    client.SelectInbox();

    List<long> uids = imap.Search(Flag.Unseen);
    foreach (long uid in uids)
    {
        IMail email = new MailBuilder()
                .CreateFromEml(imap.GetMessageByUID(uid));
        string subject = email.Subject;
   }

    client.Close();
} 

Any organization and personal accounts

To access accounts from any organization and personal accounts as well, you need to specify correct account types when you create the App in your AD:

Additionally you need to use:    

    .WithAuthority(
        AadAuthorityAudience.AzureAdAndPersonalMicrosoftAccount
        )

instead of

    .WithTenantId(tenantId)

when creating the app:

var app = ConfidentialClientApplicationBuilder
    .Create(clientId)
    .WithAuthority(
        AadAuthorityAudience.AzureAdAndPersonalMicrosoftAccount
        )
    .WithClientSecret(clientSecret)
    .WithRedirectUri("http://localhost/myapp/")
    .Build();

Token serialization

Below is a simple implementation that saves MSAL token cache to file:

static class TokenCacheHelper
{
    public static void EnableSerialization(ITokenCache tokenCache)
    {
        tokenCache.SetBeforeAccess(BeforeAccessNotification);
        tokenCache.SetAfterAccess(AfterAccessNotification);
    }

    private static readonly string _fileName = "msalcache.bin3";

    private static readonly object _fileLock = new object();


    private static void BeforeAccessNotification(TokenCacheNotificationArgs args)
    {
        lock (_fileLock)
        {
            byte[] data = null;
            if (File.Exists(_fileName))
                data = File.ReadAllBytes(_fileName);
            args.TokenCache.DeserializeMsalV3(data);
        }
    }

    private static void AfterAccessNotification(TokenCacheNotificationArgs args)
    {
        if (args.HasStateChanged)
        {
            lock (_fileLock)
            {
                byte[] data = args.TokenCache.SerializeMsalV3();
                File.WriteAllBytes(_fileName, data);
            }
        }
    }
};

Please note that most likely you should store this cache in an encrypted form in some kind of a database.
Consider using MSAL token serialization implementations available here:

https://docs.microsoft.com/en-us/azure/active-directory/develop/msal-net-token-cache-serialization

The post OAuth 2.0 web flow with Office365/Exchange IMAP/POP3/SMTP first appeared on Blog | Limilabs.

Client credential flow is now supported:

https://www.limilabs.com/blog/oauth2-client-credential-flow-office365-exchange-imap-pop3-smtp

Microsoft is working on bringing OAuth Client Credential Flow support for POP/IMAP for Office365/Exchange. It’s planned to be released in June 2022:

https://www.microsoft.com/en-us/microsoft-365/roadmap?filters=&searchterms=70577

Check out currently supported OAuth 2.0 flows

• OAuth 2.0 with Office365/Exchange IMAP/POP3/SMTP
• OAuth 2.0 password grant with Office365/Exchange IMAP/POP3/SMTP
• OAuth 2.0 device flow with Office365/Exchange IMAP/POP3/SMTP

The post Office365: Client Credential Flow support for POP/IMAP is coming in June 2022 first appeared on Blog | Limilabs.

• OAuth 2.0 with Office365/Exchange IMAP/POP3/SMTP
• OAuth 2.0 web flow with Office365/Exchange IMAP/POP3/SMTP
• OAuth 2.0 password grant with Office365/Exchange IMAP/POP3/SMTP
• OAuth 2.0 device flow with Office365/Exchange IMAP/POP3/SMTP
• OAuth 2.0 client credential flow with Office365/Exchange IMAP/POP3/SMTP

This article shows how to implement OAuth 2.0 device flow to access Office365 via IMAP, POP3 or SMTP using Mail.dll .net email client.

Device flow allows operator/administrator to authenticate your application on a different machine than your application is installed.

Make sure IMAP/POP3/SMTP is enabled for your organization and mailbox:
Enable IMAP/POP3/SMTP in Office 365

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
• email
• IMAP.AccessAsUser.All
• POP.AccessAsUser.All
• SMTP.Send

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/

string clientId = "Application (client) ID";
string tenantId = "Directory (tenant) ID";

IPublicClientApplication app = PublicClientApplicationBuilder
    .Create(clientId)
    .WithTenantId(tenantId)
    .Build();
// This allows saving access/refresh tokens to some storage
TokenCacheHelper.EnableSerialization(app.UserTokenCache);

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.Send",
};

Now acquire an access token and a user name:

string userName;
string accessToken;

var account = (await app.GetAccountsAsync()).FirstOrDefault();
try
{
    AuthenticationResult refresh = await app
        .AcquireTokenSilent(scopes, account)
        .ExecuteAsync();

    userName = refresh.Account.Username;
    accessToken = refresh.AccessToken;
}
catch (MsalUiRequiredException e)
{
    var acquire = await app.AcquireTokenWithDeviceCode(
        scopes, 
        callback=>
    {
        // Write url and code to logs so the operator can react:
        Console.WriteLine(callback.VerificationUrl);
        Console.WriteLine(callback.UserCode);

        // This happens on the first run, manually,
        //  on the operator machine.
        // The code below code is only to illustrate 
        // the operator opening browser on his machine,
        // opening the url and using the code 
        // (extracted from the application logs)
        // to authenticate the app.
        System.Diagnostics.Process.Start(
            new ProcessStartInfo(callback.VerificationUrl) 
                        { UseShellExecute = true }
            );

        return Task.CompletedTask;
    }).ExecuteAsync();

    userName = acquire.Account.Username;
    accessToken = acquire.AccessToken;
}

AcquireTokenWithDeviceCode call waits until operator/administrator gives consent by going to VerificationUrl, entering UserCode and authenticating – this usually happens on a different machine than the application is installed.

Finally your app will exit AcquireTokenWithDeviceCode method and connect using IMAP/POP3/SMTP, authenticate and download emails:

using (Imap client = new Imap())
{
    client.ConnectSSL("outlook.office365.com");
    client.LoginOAUTH2(userName, accessToken);
 
    client.SelectInbox();

    // ...

    client.Close();
} 

You can find more details on this flow here:

https://docs.microsoft.com/en-us/azure/active-directory/develop/v2-oauth2-device-code

Token serialization

Below is a simple implementation that saves MSAL token cache to file. Please note that most likely you should store this cache in an encrypted form:

static class TokenCacheHelper
{
    public static void EnableSerialization(ITokenCache tokenCache)
    {
        tokenCache.SetBeforeAccess(BeforeAccessNotification);
        tokenCache.SetAfterAccess(AfterAccessNotification);
    }

    private static readonly string _fileName = "msalcache.bin3";

    private static readonly object _fileLock = new object();


    private static void BeforeAccessNotification(TokenCacheNotificationArgs args)
    {
        lock (_fileLock)
        {
            byte[] data = null;
            if (File.Exists(_fileName))
                data = File.ReadAllBytes(_fileName);
            args.TokenCache.DeserializeMsalV3(data);
        }
    }

    private static void AfterAccessNotification(TokenCacheNotificationArgs args)
    {
        if (args.HasStateChanged)
        {
            lock (_fileLock)
            {
                byte[] data = args.TokenCache.SerializeMsalV3();
                File.WriteAllBytes(_fileName, data);
            }
        }
    }
};

More details on MSAL token serialization are available here:

https://docs.microsoft.com/en-us/azure/active-directory/develop/msal-net-token-cache-serialization

Extending Sign-in frequency with policies

You can extend how often operator needs to re-authenticate the application up to 1 year:

Side note: Have in mind that similarly a client credential flow requires a client secret which is valid for 2 years maximum.

The post OAuth 2.0 device flow with Office365/Exchange IMAP/POP3/SMTP first appeared on Blog | Limilabs.

Check ‘Turn on modern authentication…‘ for OAuth flows.

Check IMAP, POP3 and SMTP for App passwords flows.

Then go to Users screen:

Select an user and on the Mail tab click Manage email apps

Check IMAP, Pop and Authenticated SMTP to turn on the protocols for this account

Have in mind it takes 20-30 minutes for the changes to take effect.

AD configuration

In your Active Directory, make sure Enable Security defaults is set to No:

Make sure there are no Conditional Access | Policies defined in your AD:

Authentication – Basic Auth [deprecated]

It is no longer possible to re-enable Basic Auth or use App passwords.

To use basic authentication (username/password) you’ll need to
Re-enable Basic Auth for your tenant

For MFA enabled/enforced accounts you must
Create and use App passwords

using (Imap imap = new Imap())
{
    imap.ConnectSSL("outlook.office365.com");
 
    imap.UseBestLogin(
        "AdeleV@limilabs.onmicrosoft.com",  
        "password");
 
    imap.SelectInbox();

    List<long> uids = imap.Search(Flag.Unseen);
 
    foreach (long uid in uids)
    {
        IMail email = new MailBuilder()
            .CreateFromEml(imap.GetMessageByUID(uid));
        string subject = email.Subject;
    }
 
    imap.Close();
}

Authentication – OAuth 2.0

Daemons/Services: Password grant (MFA/2FA must be turned off for this account):
https://www.limilabs.com/blog/oauth2-password-grant-office365-exchange-imap-pop3-smtp

Daemons/Services: Client credential flow:
https://www.limilabs.com/blog/oauth2-client-credential-flow-office365-exchange-imap-pop3-smtp

Web apps (requires user interaction):
https://www.limilabs.com/blog/oauth2-web-flow-office365-exchange-imap-pop3-smtp

Standalone devices (requires very little interaction):
https://www.limilabs.com/blog/oauth2-device-flow-office365-exchange-imap-pop3-smtp

Desktop apps (requires user interaction):
https://www.limilabs.com/blog/oauth2-office365-exchange-imap-pop3-smtp

using (Imap imap = new Imap())
{
    imap.ConnectSSL("outlook.office365.com");
 
    imap.UseBestLogin(
        "AdeleV@limilabs.onmicrosoft.com",  
        "access-token");
 
    imap.SelectInbox();

    List<long> uids = imap.Search(Flag.Unseen);
 
    foreach (long uid in uids)
    {
        IMail email = new MailBuilder()
            .CreateFromEml(imap.GetMessageByUID(uid));
        string subject = email.Subject;
    }
 
    imap.Close();
}

Exchange administration

You can find the same mailbox/user settings through Exchange administration screens:

The post Office 365 enable IMAP/POP3 and SMTP access first appeared on Blog | Limilabs.

• OAuth 2.0 with Office365/Exchange IMAP/POP3/SMTP
• OAuth 2.0 web flow with Office365/Exchange IMAP/POP3/SMTP
• OAuth 2.0 password grant with Office365/Exchange IMAP/POP3/SMTP
• OAuth 2.0 device flow with Office365/Exchange IMAP/POP3/SMTP
• OAuth 2.0 client credential flow with Office365/Exchange IMAP/POP3/SMTP

This article shows how to implement OAuth 2.0 password grant flow to access Office365 via IMAP, POP3 or SMTP using Mail.dll .NET email client.

Enable email protocols

Make sure IMAP/POP3/SMTP is enabled for your organization and mailbox:
Enable IMAP/POP3/SMTP in Office 365

Disable MFA for account

Password grant flow requires Multi-Factor Authentication (MFA) to be disabled for this mailbox – make also sure there are no Active Directory policies that match this account and require MFA (you can of course have policies that match all other accounts).

Go to Microsoft365 admin center. Select Setup on the left menu and in the Sign-in and security section select Configure multifactor authentication (MFA):

You can use per-user MFA or AD policies.

Register and configure application

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

Enable additional flows:

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
• email
• IMAP.AccessAsUser.All
• POP.AccessAsUser.All
• SMTP.Send

Remember to Grant admin consent:

Obtain OAuth 2.0 token

Use Microsoft Authentication Library for .NET (MSAL.NET) nuget package to obtain an access token:
https://www.nuget.org/packages/Microsoft.Identity.Client/

string clientId = "Application (client) ID";
string tenantId = "Directory (tenant) ID";

string userEmail = "Username for mailbox";
string userPassword = "Password for that user";

IPublicClientApplication app = PublicClientApplicationBuilder
    .Create(clientId)
    .WithTenantId(tenantId)
    .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.Send",
};

Now acquire an access token and a user name:

string userName;
string accessToken;

var account = (await app.GetAccountsAsync()).FirstOrDefault();

try
{
    AuthenticationResult refresh = await app
        .AcquireTokenSilent(scopes, account)
        .ExecuteAsync();

    userName = refresh.Account.Username;
    accessToken = refresh.AccessToken;
}
catch (MsalUiRequiredException e)
{
    SecureString securePassword = new SecureString();
    foreach (char c in userPassword)
    {
        securePassword.AppendChar(c);
    }

    var result = await app.AcquireTokenByUsernamePassword(
        scopes, 
        userEmail, 
        securePassword).ExecuteAsync();

    userName = result.Account.Username;
    accessToken = result.AccessToken;
}

Install Mail.dll email library

The easiest way to install Mail.dll is to download it from nuget via Package Manager:

PM> Install-Package Mail.dll

Alternatively you can download Mail.dll directly from our website.

Download and process emails

Finally you can connect using IMAP/POP3/SMTP, authenticate and download user’s emails:

using (Imap client = new Imap())
{
    client.ConnectSSL("outlook.office365.com");
    client.LoginOAUTH2(userName, accessToken);
 
    client.SelectInbox();

    List<long> uids = imap.Search(Flag.Unseen);
    foreach (long uid in uids)
    {
        IMail email = new MailBuilder()
                .CreateFromEml(imap.GetMessageByUID(uid));
        string subject = email.Subject;
   }

    client.Close();
} 

The post OAuth 2.0 password grant with Office365/Exchange IMAP/POP3/SMTP first appeared on Blog | Limilabs.

• OAuth 2.0 with Office365/Exchange IMAP/POP3/SMTP
• OAuth 2.0 web flow with Office365/Exchange IMAP/POP3/SMTP
• OAuth 2.0 password grant with Office365/Exchange IMAP/POP3/SMTP
• OAuth 2.0 device flow with Office365/Exchange IMAP/POP3/SMTP
• OAuth 2.0 client credential flow with Office365/Exchange IMAP/POP3/SMTP

This article shows how to implement OAuth 2.0 desktop flow to access Office365 via IMAP, POP3 or SMTP using Mail.dll .net email client.

Make sure IMAP/POP3/SMTP is enabled for your organization and mailbox:
Enable IMAP/POP3/SMTP in Office 365

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

Remember to add authentication entries (localhost is needed for .net core):

RedirectUri

.NET desktop: https://login.microsoftonline.com/common/oauth2/nativeclient
.NET core/.NET 5,6,7+: http://localhost
ASP.NET: your application custom url

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
• email
• IMAP.AccessAsUser.All
• POP.AccessAsUser.All
• SMTP.Send

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/

string clientId = "Application (client) ID";
string tenantId = "Directory (tenant) ID";

// for @outlook.com/@hotmail accounts instead of setting .WithTenantId use:
// .WithAuthority(AadAuthorityAudience.PersonalMicrosoftAccount)

var app = PublicClientApplicationBuilder
                .Create(clientId)
                .WithTenantId(tenantId)
                .WithDefaultRedirectUri()
                .Build();
// This allows saving access/refresh tokens to some storage
TokenCacheHelper.EnableSerialization(app.UserTokenCache);

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.Send",
};

In addition, you should request 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:

string userName;
string accessToken;

var account = (await app.GetAccountsAsync()).FirstOrDefault();

try
{
    AuthenticationResult refresh = await app
        .AcquireTokenSilent(scopes, account)
        .ExecuteAsync();

    userName = refresh.Account.Username;
    accessToken = refresh.AccessToken;
}
catch (MsalUiRequiredException e)
{
    var result = await app.AcquireTokenInteractive(scopes)
        .ExecuteAsync();

    userName = result.Account.Username;
    accessToken = result.AccessToken;
}

On the first run user will see a Microsoft login screen, with option to log-in, using a known account and granting access to the app (if needed):

Finally you can connect using IMAP/POP3/SMTP, authenticate and download user’s emails:

using (Imap client = new Imap())
{
    client.ConnectSSL("outlook.office365.com");
    client.LoginOAUTH2(userName, accessToken);
 
    client.SelectInbox();

    List<long> uids = imap.Search(Flag.Unseen);
    foreach (long uid in uids)
    {
        IMail email = new MailBuilder()
                .CreateFromEml(imap.GetMessageByUID(uid));
        string subject = email.Subject;
   }

    client.Close();
} 

Any organization and personal accounts

To access accounts from any organization and personal accounts as well, you need to specify correct account types when you create the App in your AD:

Additionally you need to use:    

    .WithAuthority(
        AadAuthorityAudience.AzureAdAndPersonalMicrosoftAccount
        )

instead of

    .WithTenantId(tenantId)

when creating the app:

 var app = PublicClientApplicationBuilder
    .Create(clientId)
    .WithAuthority(
        AadAuthorityAudience.AzureAdAndPersonalMicrosoftAccount
        )
    .WithDefaultRedirectUri()
    .Build();

Token serialization

Below is a simple implementation that saves MSAL token cache to file:

static class TokenCacheHelper
{
    public static void EnableSerialization(ITokenCache tokenCache)
    {
        tokenCache.SetBeforeAccess(BeforeAccessNotification);
        tokenCache.SetAfterAccess(AfterAccessNotification);
    }

    private static readonly string _fileName = "msalcache.bin3";

    private static readonly object _fileLock = new object();


    private static void BeforeAccessNotification(TokenCacheNotificationArgs args)
    {
        lock (_fileLock)
        {
            byte[] data = null;
            if (File.Exists(_fileName))
                data = File.ReadAllBytes(_fileName);
            args.TokenCache.DeserializeMsalV3(data);
        }
    }

    private static void AfterAccessNotification(TokenCacheNotificationArgs args)
    {
        if (args.HasStateChanged)
        {
            lock (_fileLock)
            {
                byte[] data = args.TokenCache.SerializeMsalV3();
                File.WriteAllBytes(_fileName, data);
            }
        }
    }
};

Please note that most likely you should store this cache in an encrypted form in some kind of a database.
Consider using MSAL token serialization implementations available here:

https://docs.microsoft.com/en-us/azure/active-directory/develop/msal-net-token-cache-serialization

The post OAuth 2.0 with Office365/Exchange IMAP/POP3/SMTP first appeared on Blog | Limilabs.

This security enhancement ensures that receiving emails via POP3 remain safeguarded against potential threats and unauthorized access.

By default clients and POP3 servers negotiate SSL/TLS versions they can both use. Most systems don’t allow SSL 3.0, TLS 1.0, 1.1 anymore and Mail.dll POP3 component simply uses the most recent TLS version.

TLS 1.2 and 1.3 are the most secure versions of TLS protocols. It is easy to force the connection to use it.

All you need to do is to set Pop3.SSLConfiguration.EnabledSslProtocols property to SslProtocols.Tls12 before issuing ConnectSSL or Connect and StartTLS sequence:

// C#

using (Pop3 pop3 = new Pop3())
{
    pop3.SSLConfiguration.EnabledSslProtocols = SslProtocols.Tls12;

    pop3.ConnectSSL("pop.example.com");

    pop3.UseBestLogin("user","password");

    // ... 

    pop3.Close();
}

' VB .NET

Using pop3 As New Pop3()
	pop3.SSLConfiguration.EnabledSslProtocols = SslProtocols.Tls12

	pop3.ConnectSSL("pop.example.com")

	pop3.UseBestLogin("user@example.com", "password")

	'...

	pop3.Close()
End Using

For explicit SSL/TLS, code is almost the same. You first connect to a default, non-secure POP3 port and secure the connection using Pop3.StartTLS method:

// C#

using (Pop3 pop3 = new Pop3())
{
    pop3.SSLConfiguration.EnabledSslProtocols = SslProtocols.Tls12;

    pop3.Connect("pop.example.com");
    pop3.StartTLS();

    pop3.UseBestLogin("user@example.com","password");

    // ... 

    pop3.Close();
}

' VB.NET

Using pop3 As New Pop3()
	pop3.SSLConfiguration.EnabledSslProtocols = SslProtocols.Tls12

	pop3.Connect("pop.example.com")
	pop3.StartTLS()

	pop3.UseBestLogin("user@example.com", "password")

	'...

	pop3.Close()
End Using

Older .NET framework versions

To use TLS 1.2 in POP3 client at least .NET Framework 4.5+ must be installed on your machine and your application should target .NET 4.5+.

It is possible to use TLS 1.2 in applications targeting earlier .NET framework versions, but 4.5 must be installed on the machine. After you have .NET 4.5 installed, your 2.0 – 4.0 apps will use the 4.5 System.dll and you can enable TLS 1.2 using this code:

// C#

pop3.SSLConfiguration.EnabledSslProtocols = 
    (SecurityProtocolType)3072;

The post Using TLS 1.2 with .NET POP3 client first appeared on Blog | Limilabs.

Latest Office 365 version

For latest Office 365 after the service upgrade, use the following settings:

IMAP

Server: outlook.office365.com
SSL: true-implicit, true-explicit (StartTLS)
Port: 993 (default), 143 (default)
User: pat@domain.onmicrosoft.com or pat@your-domain.com

POP3

Server: outlook.office365.com
SSL: true-implicit, true-explicit (StartTLS)
Port: 995 (default), 110 (default)
User: pat@domain.onmicrosoft.com or pat@your-domain.com

SMTP

Server: outlook.office365.com
SSL: true-explicit (StartTLS)
Port: 587(default)
User: pat@domain.onmicrosoft.com or pat@your-domain.com

IMAP and POP3 servers allow both: implicit SSL/TLS and explicit SSL/TLS, so you can ConnectSSL method -or- Connect and StartTLS.

SMTP server requires explicit SSL – use Connect and StartTLS method.

Authentication

For Exchange Online/Office 365, we recommend using OAuth 2.0 flows:

Daemons/Services: Password grant (MFA/2FA must be turned off for this account):
https://www.limilabs.com/blog/oauth2-password-grant-office365-exchange-imap-pop3-smtp

Daemons/Services: Client credential flow:
https://www.limilabs.com/blog/oauth2-client-credential-flow-office365-exchange-imap-pop3-smtp

Web apps (requires user interaction):
https://www.limilabs.com/blog/oauth2-web-flow-office365-exchange-imap-pop3-smtp

Standalone devices (requires very little interaction):
https://www.limilabs.com/blog/oauth2-device-flow-office365-exchange-imap-pop3-smtp

Desktop apps (requires user interaction):
https://www.limilabs.com/blog/oauth2-office365-exchange-imap-pop3-smtp

It is no longer possible to re-enable Basic Auth or use App passwords.

// C#

using (Imap client = new Imap())
{
    client.ConnectSSL("outlook.office365.com");
    client.UseBestLogin("user@domain.onmicrosoft.com", "accesstoken");
    ...
}

using (Pop3 client = new Pop3())
{
    client.ConnectSSL("outlook.office365.com");
    client.UseBestLogin("user@domain.onmicrosoft.com", "accesstoken");
    ...
}

using (Smtp client = new Smtp ())
{
    client.Connect("outlook.office365.com");
    client.StartTLS();

    client.UseBestLogin("user@domain.onmicrosoft.com", "accesstoken");
    ...
}

' VB.NET

Using client As New Imap()
	client.ConnectSSL("outlook.office365.com")
	client.UseBestLogin("user@domain.onmicrosoft.com", "accesstoken")
	...
End Using

Using client As New Pop3()
	client.ConnectSSL("outlook.office365.com")
	client.UseBestLogin("user@domain.onmicrosoft.com", "accesstoken")
	...
End Using

Using client As New Smtp()
	client.Connect("outlook.office365.com")
	client.StartTLS()

	client.UseBestLogin("user@domain.onmicrosoft.com", "accesstoken")
	...
End Using

Office 365 pre-upgrade

For latest Office 365 pre-upgrade, use the following settings:

On the main screen go to “Options” / “See All Options…”:

Now click the “Settings for POP, IMAP, and SMTP access…” link:

You can find POP, SMTP and IMAP server addresses and settings on the popup window:

Office365 uses default ports for IMAP, POP3 and SMTP protocols. That means that you don’t need to remember port numbers, as Mail.dll .NET email component is going to use correct port numbers by default.

IMAP

Server: podXXXX.outlook.com
SSL: true-implicit
Port: 993 (default)
User: pat@domain.onmicrosoft.com or pat@your-domain.com

POP3

Server: podXXXX.outlook.com
SSL: true-implicit
Port: 995 (default)
User: pat@domain.onmicrosoft.com or pat@your-domain.com

SMTP

Server: podXXXX.outlook.com
SSL: true-explicit
Port: 587 (default)
User: pat@domain.onmicrosoft.com or pat@your-domain.com

You can find more details about using implicit and explicit SSL or TLS with email protocols:

• Using SSL with IMAP
• Using SSL with POP3
• Using SSL with SMTP

The post Outlook365: IMAP, POP3, and SMTP settings first appeared on Blog | Limilabs.