Securing Outlook for iOS and Android in Exchange Online

Outlook for iOS and Android provides users the fast, intuitive email and calendar experience that users expect from a modern mobile app, while being the only app to provide support for the best features of Microsoft 365 or Office 365.

Protecting company or organizational data on users' mobile devices is extremely important. Begin by reviewing Setting up Outlook for iOS and Android, to ensure your users have all the required apps installed. After that, choose one of the following options to secure your devices and your organization's data:

1. Recommended: If your organization has an Enterprise Mobility + Security subscription, or has separately obtained licensing for Microsoft Intune and Microsoft Entra ID P1 or P2, follow the steps in Leveraging Enterprise Mobility + Security suite to protect corporate data with Outlook for iOS and Android to protect corporate data with Outlook for iOS and Android.
2. If your organization doesn't have an Enterprise Mobility + Security subscription or licensing for Microsoft Intune and Microsoft Entra ID P1 or P2, follow the steps in Leveraging Basic Mobility and Security for Microsoft 365, and use the Basic Mobility and Security capabilities that are included in your Office 365 or Microsoft 365 subscription.
3. Follow the steps in Leveraging Exchange Online mobile device policies to implement basic Exchange mobile device mailbox and device access policies.

If, on the other hand, you don't want to use Outlook for iOS and Android in your organization, see Blocking Outlook for iOS and Android.

See Exchange Web Services (EWS) application policies later in this article if you'd rather implement an EWS application policy to manage mobile device access in your organization.

Setting up Outlook for iOS and Android

For devices enrolled in a unified endpoint management (UEM) solution, users will utilize the UEM solution, like the Intune Company Portal, to install the required apps: Outlook for iOS and Android and Microsoft Authenticator.

For devices that are not enrolled in an UEM solution, users need to install:

• Outlook for iOS and Android via the Apple App Store or Google Play Store
• Microsoft Authenticator app via the Apple App Store or Google Play Store
• Intune Company Portal app via Apple App Store or Google Play Store

Once the app is installed, users can follow these steps to add their corporate email account and configure basic app settings:

• Set up email account in Outlook for iOS mobile app
• Set up email in the Outlook for Android app
• Optimizing the Outlook mobile app for your iOS or Android phone

To leverage app-based conditional access policies, the Microsoft Authenticator app must be installed on iOS devices. For Android devices, the Intune Company Portal app is required. For more information, see App-based Conditional Access with Intune.

Leveraging Enterprise Mobility + Security suite to protect corporate data with Outlook for iOS and Android

The Allow/Block/Quarantine (ABQ) list provides no security guarantees (if a client spoofs the DeviceType header, it might be possible to bypass blocking for a particular device type). To securely restrict access to specific device types, we recommend that you configure conditional access policies. For more information, see App-based conditional access with Intune.

The richest and broadest protection capabilities for Microsoft 365 and Office 365 data are available when you subscribe to the Enterprise Mobility + Security suite, which includes Microsoft Intune and Microsoft Entra ID P1 or P2 features, such as conditional access. At a minimum, you will want to deploy a conditional access policy that only allows connectivity to Outlook for iOS and Android from mobile devices and an Intune app protection policy that ensures the corporate data is protected.

While the Enterprise Mobility + Security suite subscription includes both Microsoft Intune and Microsoft Entra ID P1 or P2, customers can purchase Microsoft Intune licenses and Microsoft Entra ID P1 or P2 licenses separately. All users must be licensed in order to leverage the conditional access and Intune app protection policies that are discussed in this article.

Block all email apps except Outlook for iOS and Android using conditional access

When an organization decides to standardize how users access Exchange data, using Outlook for iOS and Android as the only email app for end users, they can configure a conditional access policy that blocks other mobile access methods. To do this, you will need several conditional access policies, with each policy targeting all potential users. These policies are described in Conditional Access: Require approved client apps or app protection policy.

Follow the steps in Require approved client apps or app protection policy with mobile devices. This policy allows Outlook for iOS and Android, but blocks OAuth and basic authentication capable Exchange ActiveSync mobile clients from connecting to Exchange Online.

Note This policy ensures mobile users can access all Microsoft 365 endpoints using the applicable apps.

After the conditional access policies are enabled, it may take up to 6 hours for any previously connected mobile device to become blocked.

When the user authenticates in Outlook for iOS and Android, Exchange Online mobile device access rules (allow, block, or quarantine) are skipped if there are any Microsoft Entra Conditional Access policies applied to the user that include:

• Cloud app condition: Exchange Online or Office 365
• Device platform condition: iOS and/or Android
• Client apps condition: Mobile apps and desktop client
• One of the following Grant access controls: Require device to be marked as compliant, Require approved client app or Require app protection policy.

To leverage app-based conditional access policies, the Microsoft Authenticator app must be installed on iOS devices. For Android devices, the Intune Company Portal app is required. For more information, see App-based Conditional Access with Intune.

Protect corporate data in Outlook for iOS and Android using Intune app protection policies

App Protection Policies (APP) define which apps are allowed and the actions they can take with your organization's data. The choices available in APP enable organizations to tailor the protection to their specific needs. For some, it may not be obvious which policy settings are required to implement a complete scenario. To help organizations prioritize mobile client endpoint hardening, Microsoft has introduced taxonomy for its APP data protection framework for iOS and Android mobile app management.

The APP data protection framework is organized into three distinct configuration levels, with each level building off the previous level:

• Enterprise basic data protection (Level 1) ensures that apps are protected with a PIN and encrypted and performs selective wipe operations. For Android devices, this level validates Android device attestation. This is an entry level configuration that provides similar data protection control in Exchange Online mailbox policies and introduces IT and the user population to APP.
• Enterprise enhanced data protection (Level 2) introduces APP data leakage prevention mechanisms and minimum OS requirements. This is the configuration that is applicable to most mobile users accessing work or school data.
• Enterprise high data protection (Level 3) introduces advanced data protection mechanisms, enhanced PIN configuration, and APP Mobile Threat Defense. This configuration is desirable for users that are accessing high risk data.

To see the specific recommendations for each configuration level and the minimum apps that must be protected, review Data protection framework using app protection policies.

Regardless of whether the device is enrolled in an UEM solution, an Intune app protection policy needs to be created for both iOS and Android apps, using the steps in How to create and assign app protection policies. These policies, at a minimum, must meet the following conditions:

1. They include all Microsoft mobile applications, such as Edge, OneDrive, Office, or Teams, as this will ensure that users can access and manipulate work or school data within any Microsoft app in a secure fashion.
2. They are assigned to all users. This ensures that all users are protected, regardless of whether they use Outlook for iOS or Android.
3. Determine which framework level meets your requirements. Most organizations should implement the settings defined in Enterprise enhanced data protection (Level 2) as that enables data protection and access requirements controls.

To apply Intune app protection policies against apps on Android devices that are not enrolled in Intune, the user must also install the Intune Company Portal. For more information, see What to expect when your Android app is managed by app protection policies.

Leveraging Basic Mobility and Security for Microsoft 365

If you don't plan to leverage the Enterprise Mobility + Security suite, you can use Basic Mobility and Security for Microsoft 365. This solution requires that mobile devices be enrolled. When a user attempts to access Exchange Online with a device that is not enrolled, the user is blocked from accessing the resource until they enroll the device.

Because this is a device management solution, there is no native capability to control which apps can be used even after a device is enrolled. If you want to limit access to Outlook for iOS and Android, you will need to obtain Microsoft Entra ID P1 or P2 licenses and leverage the conditional access policies discussed in Block all email apps except Outlook for iOS and Android using conditional access.

An admin who is assigned the Directory writers role must complete the following steps to activate and set up enrollment. See Set up Basic Mobility and Security for complete steps. In summary, these steps include:

1. Activating Basic Mobility and Security by following the steps in the Microsoft 365 Security Center.
2. Setting up unified endpoint management by, for example, creating an APNs certificate to manage iOS devices.
3. Creating device policies and apply them to groups of users. When you do this, your users will get an enrollment message on their device. And when they've completed enrollment, their devices will be restricted by the policies you've set up for them.

Policies and access rules created in Basic Mobility and Security will override both Exchange mobile device mailbox policies and device access rules created in the Exchange admin center. After a device is enrolled in Basic Mobility and Security, any Exchange mobile device mailbox policy or device access rule that is applied to that device will be ignored.

Leveraging Exchange Online mobile device policies

If you don't plan on leveraging either the Enterprise Mobility + Security suite or the Basic Mobility and Security functionality, you can implement an Exchange mobile device mailbox policy to secure the device, and device access rules to limit device connectivity.

Mobile device mailbox policy

Outlook for iOS and Android supports the following mobile device mailbox policy settings in Exchange Online:

• Device encryption enabled
• Min password length (only on Android)
• Password enabled
• Allow Bluetooth (used to manage the Outlook for Android wearable app)
  • When AllowBluetooth is enabled (default behavior) or configured for HandsfreeOnly, wearable synchronization between Outlook on the Android device and Outlook on the wearable is allowed for the work or school account.
  • When AllowBluetooth is disabled, Outlook for Android will disable synchronization between Outlook on the Android device and Outlook on the wearable for the specified work or school account (and delete any data previously synced for the account). Disabling the synchronization is controlled entirely within Outlook itself; Bluetooth is not disabled on the device or wearable nor is any other wearable app affected.

  For information on how to create or modify an existing mobile device mailbox policy, see Mobile device mailbox policies in Exchange Online.

  In addition, Outlook for iOS and Android supports Exchange Online's device-wipe capability. With Outlook, a remote wipe only wipes data within the Outlook app itself and does not trigger a full device wipe. For more information on how to perform a remote wipe, see Perform a remote wipe on a mobile phone in Exchange Online.

  Device access policy

  Outlook for iOS and Android should be enabled by default, but in some existing Exchange Online environments the app may be blocked for a variety of reasons. Once an organization decides to standardize how users access Exchange data and use Outlook for iOS and Android as the only email app for end users, you can configure blocks for other email apps running on users' iOS and Android devices. You have two options for instituting these blocks within Exchange Online: the first option blocks all devices and only allows usage of Outlook for iOS and Android; the second option allows you to block individual devices from using the native Exchange ActiveSync apps.

  Because device IDs are not governed by any physical device ID, they can change without notice. When this happens, it can cause unintended consequences when device IDs are used for managing user devices, as existing 'allowed' devices may be unexpectedly blocked or quarantined by Exchange. Therefore, we recommend administrators only set mobile device access policies that allow/block devices based on device type or device model.

  Option 1: Block all email apps except Outlook for iOS and Android

  You can define a default block rule and then configure an allow rule for Outlook for iOS and Android, and for Windows devices, using the following Exchange Online PowerShell commands. This configuration will prevent any Exchange ActiveSync native app from connecting, and will only allow Outlook for iOS and Android.

  Create the default block rule:

  Set-ActiveSyncOrganizationSettings -DefaultAccessLevel Block 

  New-ActiveSyncDeviceAccessRule -Characteristic DeviceModel -QueryString "Outlook for iOS and Android" -AccessLevel Allow 

  Option 2: Block native Exchange ActiveSync apps on Android and iOS devices

  Alternatively, you can block native Exchange ActiveSync apps on specific Android and iOS devices or other types of devices.

  Confirm that there are no Exchange ActiveSync device access rules in place that block Outlook for iOS and Android:

  Get-ActiveSyncDeviceAccessRule | Where-Object < $_.AccessLevel -eq "Block" -and $_.QueryString -like "Outlook*" >| Format-Table Name, AccessLevel, QueryString -AutoSize 

  If any device access rules that block Outlook for iOS and Android are found, type the following to remove them:

  Get-ActiveSyncDeviceAccessRule | Where-Object < $_.AccessLevel -eq "Block" -and $_.QueryString -like "Outlook*" >| Remove-ActiveSyncDeviceAccessRule 

  New-ActiveSyncDeviceAccessRule -Characteristic DeviceType -QueryString "Android" -AccessLevel Block New-ActiveSyncDeviceAccessRule -Characteristic DeviceType -QueryString "iPad" -AccessLevel Block New-ActiveSyncDeviceAccessRule -Characteristic DeviceType -QueryString "iPhone" -AccessLevel Block New-ActiveSyncDeviceAccessRule -Characteristic DeviceType -QueryString "iPod" -AccessLevel Block 

  Get-MobileDevice | Select-Object DeviceOS,DeviceModel,DeviceType | Export-CSV c:\temp\easdevices.csv 

  New-ActiveSyncDeviceAccessRule -Characteristic DeviceType -QueryString "HTCOne" -AccessLevel Block 

  Note The -QueryString parameter does not accept wildcards or partial matches.

  Additional resources:

  • New-ActiveSyncDeviceAccessRule
  • Get-MobileDevice
  • Set-ActiveSyncOrganizationSettings

  Blocking Outlook for iOS and Android

  If you don't want users in your organization to access Exchange data with Outlook for iOS and Android, the approach you take depends on whether you are using Microsoft Entra Conditional Access policies or Exchange Online's device access policies.

  Option 1: Block mobile device access using a conditional access policy

  Microsoft Entra Conditional Access does not provide a mechanism whereby you can specifically block Outlook for iOS and Android while allowing other Exchange ActiveSync clients. With that said, conditional access policies can be used to block mobile device access in two ways:

  • Option A: Block mobile device access on both the iOS and Android platforms
  • Option B: Block mobile device access on a specific mobile device platform

  Option A: Block mobile device access on both the iOS and Android platforms

  If you want to prevent mobile device access for all users, or a subset of users, using conditional access, follow these steps.

  Create conditional access policies, with each policy either targeting all users or a subset of users via a security group. Details are in Common Conditional Access policy: Require approved client apps or app protection policy.

  1. The first policy blocks Outlook for iOS and Android and other OAuth capable Exchange ActiveSync clients from connecting to Exchange Online. See "Step 1 - Configure a Microsoft Entra Conditional Access policy for Exchange Online," but for the fifth step, choose Block access.
  2. The second policy prevents Exchange ActiveSync clients leveraging basic authentication from connecting to Exchange Online. See "Step 2 - Configure a Microsoft Entra Conditional Access policy for Exchange Online with ActiveSync (EAS)."

  Option B: Block mobile device access on a specific mobile device platform

  If you want to prevent a specific mobile device platform from connecting to Exchange Online, while allowing Outlook for iOS and Android to connect using that platform, create the following conditional access policies, with each policy targeting all users. Details are in Common Conditional Access policy: Require approved client apps or app protection policy.

  1. The first policy allows Outlook for iOS and Android on the specific mobile device platform and blocks other OAuth capable Exchange ActiveSync clients from connecting to Exchange Online. See "Step 1 - Configure a Microsoft Entra Conditional Access policy for Exchange Online," but for step 4a, select only the desired mobile device platform (such as iOS) to which you want to allow access.
  2. The second policy blocks the app on the specific mobile device platform and other OAuth capable Exchange ActiveSync clients from connecting to Exchange Online. See "Step 1 - Configure a Microsoft Entra Conditional Access policy for Exchange Online," but for step 4a, select only the desired mobile device platform (such as Android) to which you want to block access, and for step 5, choose Block access.
  3. The third policy prevents Exchange ActiveSync clients leveraging basic authentication from connecting to Exchange Online. See "Step 2 - Configure a Microsoft Entra Conditional Access policy for Exchange Online with ActiveSync (EAS)."

  Option 2: Block Outlook for iOS and Android using Exchange mobile device access rules

  If you are managing your mobile device access via Exchange Online's device access rules, you have two options:

  • Option A: Block Outlook for iOS and Android on both the iOS and Android platforms
  • Option B: Block Outlook for iOS and Android on a specific mobile device platform

  Every Exchange organization has different policies regarding security and device management. If an organization decides that Outlook for iOS and Android doesn't meet their needs or is not the best solution for them, administrators have the ability to block the app. Once the app is blocked, mobile Exchange users in your organization can continue accessing their mailboxes by using the built-in mail applications on iOS and Android.

  The New-ActiveSyncDeviceAccessRule cmdlet has a Characteristic parameter, and there are three Characteristic options that administrators can use to block the Outlook for iOS and Android app. The options are UserAgent, DeviceModel, and DeviceType. In the two blocking options described in the following sections, you will use one or more of these characteristic values to restrict the access that Outlook for iOS and Android has to the mailboxes in your organization.

  The values for each characteristic are displayed in the following table:

  Characteristic	String for iOS	String for Android
  DeviceModel	Outlook for iOS and Android	Outlook for iOS and Android
  DeviceType	Outlook	Outlook
  UserAgent	Outlook-iOS/2.0	Outlook-Android/2.0

  Option A: Block Outlook for iOS and Android on both the iOS and Android platforms

  With the New-ActiveSyncDeviceAccessRule cmdlet, you can define a device access rule, using either the DeviceModel or DeviceType characteristic. In both cases, the access rule blocks Outlook for iOS and Android across all platforms, and will prevent any device, on both the iOS platform and Android platform, from accessing an Exchange mailbox via the app.

  The following are two examples of a device access rule. The first example uses the DeviceModel characteristic; the second example uses the DeviceType characteristic.

  New-ActiveSyncDeviceAccessRule -Characteristic DeviceType -QueryString "Outlook" -AccessLevel Block 

  New-ActiveSyncDeviceAccessRule -Characteristic DeviceModel -QueryString "Outlook for iOS and Android" -AccessLevel Block 

  Option B: Block Outlook for iOS and Android on a specific mobile device platform

  With the UserAgent characteristic, you can define a device access rule that blocks Outlook for iOS and Android across a specific platform. This rule will prevent a device from using Outlook for iOS and Android to connect on the platform you specify. The following examples show how to use the device-specific value for the UserAgent characteristic.

  To block Android and allow iOS:

  New-ActiveSyncDeviceAccessRule -Characteristic UserAgent -QueryString "Outlook-Android/2.0" -AccessLevel Block New-ActiveSyncDeviceAccessRule -Characteristic UserAgent -QueryString "Outlook-iOS/2.0" -AccessLevel Allow 

  To block iOS and allow Android:

  New-ActiveSyncDeviceAccessRule -Characteristic UserAgent -QueryString "Outlook-Android/2.0" -AccessLevel Allow New-ActiveSyncDeviceAccessRule -Characteristic UserAgent -QueryString "Outlook-iOS/2.0" -AccessLevel Block 

  Exchange Online controls

  Beyond Microsoft Endpoint Manager, Basic Mobility and Security for Microsoft 365, and Exchange mobile device policies, you can manage the access that mobile devices have to information in your organization through various Exchange Online controls, as well as, whether to allow users access to add-ins within Outlook for iOS and Android.

  Exchange Web Services (EWS) application policies

  An EWS application policy can control whether or not applications are allowed to leverage the REST API. Note that when you configure an EWS application policy that only allows specific applications access to your messaging environment, you must add the user-agent string for Outlook for iOS and Android to the EWS allow list.

  The following example shows how to add the user-agent strings to the EWS allow list:

  Set-OrganizationConfig -EwsAllowList @ 

  Exchange User controls

  With the native Microsoft sync technology, administrators can control usage of Outlook for iOS and Android at the mailbox level. By default, users are allowed to access mailbox data using Outlook for iOS and Android. The following example shows how to disable a user's mailbox access with Outlook for iOS and Android:

  Set-CASMailbox jane@contoso.com -OutlookMobileEnabled $false 

  Managing add-ins

  Outlook for iOS and Android lets users integrate popular apps and services with the email client. Add-ins for Outlook are available on the web, Windows, Mac, and mobile. Since add-ins are managed via Microsoft 365 or Office 365, users are able to share data and messages between Outlook for iOS and Android and the unmanaged add-in (even when the account is managed by an Intune App Protection policy), unless add-ins are turned off for the user within the Microsoft 365 admin center.

  If you want to stop your end users from accessing and installing Outlook add-ins (which affects all Outlook clients), execute the following changes to roles in the Microsoft 365 admin center:

  • To prevent users from installing Office Store add-ins, remove the My Marketplace role from them.
  • To prevent users from side loading add-ins, remove the My Custom Apps role from them.
  • To prevent users from installing all add-ins, remove both, My Custom Apps and My Marketplace roles from them.