Product Documentation

Email Strategy

Jan 12, 2017

Secure access to email from mobile devices is one of the main drivers behind any organization's mobility management initiative. Deciding on the proper email strategy is often a key component of any XenMobile design. XenMobile offers several options to accommodate different use cases, based on security, user experience, and integration requirements. This article covers the typical design decision process and considerations for choosing the right solution, from client selection to mail traffic flow.

Choosing Your Email Clients

Client selection is generally at the top of the list when it comes to the overall email strategy design. You can choose from a number of clients, including Citrix Secure Mail, native mail that is included with a particular mobile platform operating system, or other third-party clients available through the public app stores. Depending on your needs, you can possibly support the user communities with a single (standard) client or you may need to use a combination of clients.

The following table outlines design considerations for the different client options available:

 Topic

Secure Mail

Native (for example, iOS Mail)

Third-party (for example, TouchDown)

Minimum XenMobile Edition

Advanced

MDM

MDM

Configuration

Exchange account profiles configured via an MDX policy.

Exchange account profiles configured via an MDM policy.

Note: Android support is limited to: SAFE/KNOX, HTC, and Android for Work. All other clients are considered third-party clients.

Generally requires manual configuration by the user.

Configuration of Exchange account profiles via an MDM policy for TouchDown only.

Security

Secure by design.

Security with MDX policies with added data encryption levels.

Fully managed app via an MDX policy.

Added layer of authentication with Citrix PIN.

Highest security.

Based on vendor/app feature set.

Makes use of device encryption settings (with no security via MDX policies).

Relies on device-level authentication for access to the app.

Higher security.

Based on vendor/app feature set.

High security.

Integration

Allows interaction with managed (MDX) apps by default.

Open web URLs with Citrix Secure Web (intranet access).

ShareFile integration (save to/attach from).

GoToMeeting direct join/dial-in.

WorxChat (Lync presence).

Can only interact with other unmanaged (non-MDX) apps by default.

 

Can only interact with other unmanaged (non-MDX) apps by default.

 

Deployment/ Licensing

You may push Secure Mail through MDM or make Secure Mail available as a self-service app from the XenMobile Store.

Included with XenMobile Advanced and Enterprise licensing.

Client app included with platform operating system.

No additional licensing requirements.

Can pushed via MDM, as an enterprise app or directly from public app stores.

Associated licensing model/costs based on app vendor.

Support

Single vendor support for the client and EMM solution (Citrix).

Embedded support contact info in Secure Hub/app debug logging capabilities.

One client to support.

Vendor defined support (Apple/Google).

May need to support different clients based on device platform.

Vendor-defined support

One client to support, assuming that the third-party client is supported on all managed device platforms.

Mail traffic flow and filtering considerations

This section discusses the three main scenarios and design considerations with regard to the flow of mail (ActiveSync) traffic in the context of XenMobile.

Scenario 1: Exposed Exchange

It is common for environments that support external clients to have Exchange ActiveSync services exposed to the Internet. Mobile ActiveSync clients connect through this externally facing path through a reverse proxy (for example, NetScaler) or through an edge server. This option is required for the use of native or third-party mail clients, making these clients the popular choice when it comes to this scenario. Although not a common practice, you could also use the Secure Mail client in this scenario. By doing so, you benefit from the security features offered by the use of MDX policies and management of the app.

Scenario 2: Tunneled via NetScaler (micro VPN and STA)

This is the default scenario when using the Secure Mail client given its micro VPN capabilities. In this case, the Secure Mail client establishes a secure connection to ActiveSync via NetScaler Gateway. In essence, you can consider Secure Mail to be the client connecting directly to ActiveSync from the internal network. In many cases, Citrix customers are standardizing on Secure Mail as the mobile ActiveSync client of choice, as part of an initiative to eliminate the need to expose ActiveSync services to the Internet, as described in the first scenario, on an exposed Exchange Server.

Only managed (MDX wrapped) apps can use the micro VPN function. Therefore, this scenario does not apply to native clients. Even though it may be possible to wrap third-party clients with the MDX Toolkit, this practice is not common. The use of device-level VPN clients to allow tunneled access for native or third-party clients has proven to be cumbersome and not a viable solution.

Scenario 3: Cloud-hosted Exchange services

Cloud-hosted Exchange services, such as Microsoft Office 365, are becoming more popular. In the context of XenMobile, this scenario may be treated in the same way as the first scenario, because the ActiveSync service is exposed to the Internet as well. In this case, the client choices are dictated by the cloud service provider requirements, but the choices generally include support for most ActiveSync clients like Secure Mail and other native or third-party clients.

XenMobile can add value in three areas when it comes to this scenario: 

  • Client wrapping with MDX policies and app management with Secure Mail
  • Client configuration with the use of an MDM policy on supported clients (native, such as TouchDown)
  • ActiveSync filtering options with the use of XenMobile Mail Manager

Mail traffic filtering considerations

As with most services exposed to the Internet, you must secure the path and provide filtering for authorized access. The XenMobile solution includes two components designed specifically to provide ActiveSync filtering capabilities for native and third-party clients: XenMobile NetScaler Connector and XenMobile Mail Manager.

XenMobile NetScaler Connector

The use of XenMobile NetScaler Connector provides ActiveSync filtering at the perimeter, through the use of NetScaler as a proxy for ActiveSync traffic. This means that the filtering component sits in the path of mail traffic flow, intercepting mail as it enters or leaves the environment. XenMobile NetScaler Connector acts an intermediary between NetScaler and the XenMobile server. When a device attempts communication to Exchange via the ActiveSync virtual server on the NetScaler, the NetScaler performs a HTTP callout to the XenMobile NetScaler Connector service, which then checks the device status with XenMobile. Based on the status of the device, XenMobile NetScaler Connector replies to NetScaler to either allow or deny the connection. You may also configure static rules to filter access based on user, agent, and device type or ID.

This setup allows Exchange ActiveSync services to be exposed to the Internet with an added layer of security to prevent unauthorized access. Design considerations include the following: 

  • Windows Server: The XenMobile NetScaler Connector component will require the deployment of a Windows Server.
  • Filtering rule set: XenMobile NetScaler Connector is designed for filtering based on device state and information, rather than user information. Although you may configure static rules to filter by user ID, no options exist for filtering based on Active Directory group membership, for example. If there is a requirement for Active Directory group filtering, you may use XenMobile Mail Manager instead.
  • NetScaler scalability: Given the requirement to proxy ActiveSync traffic via NetScaler, proper sizing of the NetScaler instance is critical to support the added workload of all ActiveSync SSL connections.
  • NetScaler Integrated Caching: The XenMobile NetScaler Connector configuration on the NetScaler leverages the Integrated Caching function in order to cache responses from XenMobile NetScaler Connector. This eliminates the need for the NetScaler to issue a request to XenMobile NetScaler Connector for every ActiveSync transaction in a given session; it is also critical for adequate performance and scale. Integrated Caching is available with the NetScaler Platinum Edition or may be licensed separately for Enterprise Editions.
  • Custom filtering policies: You may need to create custom NetScaler policies to restrict certain ActiveSync clients outside of the standard native mobile clients. This configuration requires knowledge on ActiveSync HTTP requests and NetScaler responder policy creation.
  • Secure Mail clients: Secure Mail has micro VPN capabilities which eliminate the need for filtering at the perimeter. The Secure Mail client would generally be treated as an internal (trusted) ActiveSync client when connected through the NetScaler Gateway. In the event that support for both native and third-party (with XenMobile NetScaler Connector) and Secure Mail clients is required, Citrix recommends that Secure Mail traffic does not flow via the NetScaler virtual server used for XenMobile NetScaler Connector. You can accomplish this traffic flow via DNS and keep the XenMobile NetScaler Connector policy from affecting Secure Mail clients. 

For a diagram of XenMobile NetScaler Connector in a XenMobile deployment, see Reference Architecture for On-Premises Deployments.

XenMobile Mail Manager

XenMobile Mail Manager is a XenMobile component that provides ActiveSync filtering at the Exchange service level. This means that filtering only occurs once the mail reaches the exchange service, rather than as soon as it enters the XenMobile environment. XenMobile Mail Manager uses PowerShell to query Exchange ActiveSync for device partnership information and control access through device quarantine actions, where devices are taken in and out of quarantine based on XenMobile Mail Manager rule criteria. Similar to XenMobile NetScaler Connector, XenMobile Mail Manager checks the device status with XenMobile in order to filter access based on device compliance. You may also configure static rules to filter access based on device type or ID, agent version, and Active Directory group membership.

This solution does not require the use of NetScaler. You can deploy XenMobile Mail Manager without making any changes in terms of routing for the existing ActiveSync traffic. Design considerations include: 

  • Windows Server: The XenMobile Mail Manager component requires you to deploy Windows Server.
  • Filtering rule set: Just like XenMobile NetScaler Connector, XenMobile Mail Manager includes filtering rules to evaluate device state and. Additionally, XenMobile Mail Manager also supports static rules to filter based on Active Directory group membership.
  • Exchange integration: XenMobile Mail Manager requires direct access to the Exchange Client Access Server (CAS) hosting the ActiveSync role and control over device quarantine actions. This may present a challenge depending on the environment's architecture and security posture, so it is critical that you evaluate this technical requirement up front.
  • Other ActiveSync clients: Because XenMobile Mail Manager is filtering at the ActiveSync service level, you need to take into consideration other ActiveSync clients outside the XenMobile environment. You can configure XenMobile Mail Manager static rules to avoid unintended impact to other ActiveSync clients.
  • Extended Exchange functions: Through direct integration with Exchange ActiveSync, XenMobile Mail Manager provides the ability for XenMobile to perform an Exchange ActiveSync wipe on a mobile device. XenMobile Mail Manager also allows XenMobile to access information about Blackberry devices, and to perform control operations, such as wipe and reset password. 

For a diagram of XenMobile Mail Manager in a XenMobile deployment, see Reference Architecture for On-Premises Deployments.

Email Platform Decision Tree

The following figure helps you distinguish the pros and cons between using native email or Secure Mail solutions in your XenMobile deployment. Each choice allows for associated XenMobile options and requirements to enable server, network, and database access. The pros and cons include details on security, policy, and user interface considerations.

localized image