Office 365 ProPlus Deployment and Proxy Server Guidance
Published Sep 11 2019 10:00 AM 46.7K Views

By far, the most important prerequisite for successful Office 365 ProPlus deployment is network configuration. 


Unlike older versions of Office, Office 365 ProPlus was designed from the ground up to work with cloud services such as Microsoft Content Delivery Network (CDN).  Microsoft recommends IT Pros “Bypass or white list endpoints on network devices and services that perform traffic interception, SSL decryption, deep packet inspection and content filtering” when accessing Microsoft Office 365 service endpoints.  


We often find customers apply “legacy” network configurations for on-premises only products to Office 365 ProPlus which can lead to slower product adoption, poor product performance, and higher cost of ownership.  The network requirements are documented in Office 365 URLs and IP address ranges document.


The goal of this blog is to clarify how IT Pros can optimize Office 365 ProPlus deployments with a proxy server in order to leverage a new concept called Hybrid or “Lean Installs”.


In terms of Office 365 ProPlus general deployment, we have several broad approaches. We’re going to focus on the 3rd option, "SCCM with Office CDN fallback" or "Lean Install".


  • On-premises only – download and mirror all content from CDN on-premises. Enterprise customers have a variety of install packages (Base Office, Visio, Project, Visio + Project, second installs for languages).  All Office 365 ProPlus builds are cumulative and are updated monthly which can make this cumbersome and difficult to maintain as each permutation requires refreshed content.
  • Cloud only – installations from the Office portal and update workflow occur using CDN. End users in the enterprise are normally not Administrators so self-service installations from are blocked.  Further, installation from CDN doesn’t currently support custom configuration files to exclude applications and so forth.
  • SCCM with Office CDN fallback or “Lean Install” – IT Pros use SCCM (which has elevated permissions and allows custom configuration.xml files) to deploy Office 365 ProPlus but can either omit all or portions of the installation source and use CDN content.

SCCM is not a requirement to adopt “Lean Install” approach.  If you are using 3rd party deployment tool, identify user context of process using process monitor and adopt proxy strategy below.SCCM is not a requirement to adopt “Lean Install” approach. If you are using 3rd party deployment tool, identify user context of process using process monitor and adopt proxy strategy below.

Lean install examples:

1st Install

SCCM package contains all Office 365 ProPlus content and only subset of languages. You support 12 languages but only include two primary languages in the application source to minimize content and include AllowCdnFallback as Enabled within configuration.xml.  During the Office 365 ProPlus installation process, the Office Deployment Tool (ODT) looks first for source files in local working directory. If the language pack files required aren’t available in local source location and the AllowCdnFallback setting within configuration.xml is set to True, then the ODT will leverage the Office CDN for the missing ones.


2nd Install

Office may need to be reconfigured to make changes to Office deployments without changing the version, like adding a language or Project/V.... In this case, we only want the required bits to perform the change and nothing else.


All example scenarios above depend on the CDN to fetch content when embracing these new “Lean Install” approaches.  The primary reason we want to lean on the CDN is because it allows Office 365 ProPlus to only download the bits it requires for the change request resulting in the smallest network payload possible. 


Exploring 2nd Install Scenario in detail in terms of content size:

IT Pro wants to perform a 2nd install to add Project to an existing Office 365 ProPlus installation on one machine. 


If we use SCCM on-premises only strategy:

SCCM will download full Office content from CDN ~2GB.  SCCM will then copy this content to all distribution points to support scenario.  Let’s assume an enterprise customer has 50 distribution points, 2 GB * 50 = 100 GB per month every month (build needs to be up to date as to not downgrade client introducing security concerns).  Office 365 ProPlus builds are cumulative, irrespective of channel, so this content changes each month.


If we use SCCM with Office CDN fallback:

SCCM calls ODT Setup.exe /configure to add Project, only ~41 MB will be downloaded from CDN instead of ~2GB (without language packs). 

Make sure to use MatchInstalled parameter in your XML.  Ensure Delivery Optimization is working for further efficiency.Make sure to use MatchInstalled parameter in your XML. Ensure Delivery Optimization is working for further efficiency.

We expect most customers will download and cache all Office 365 ProPlus content one time to existing machines to perform an upgrade to Office 365 ProPlus but once installed we recommend to leverage the lean technique going forward.

Having “lean” applications in SCCM also means they rarely need to be updated.  An occasional refresh of the Office Deployment Tool (ODT) is good idea. (Less than 10 MB)Having “lean” applications in SCCM also means they rarely need to be updated. An occasional refresh of the Office Deployment Tool (ODT) is good idea. (Less than 10 MB)

Tip: There are several ODT features which can benefit from approach (FallbacktoCDN, MatchPreviousMSI, MatchInstalled, MatchOS)


Proxy Challenge

It seems there are an infinite number of ways customers secure egress traffic to internet for security and compliance.  Some don't configure a proxy within Windows and some do.  The Office team is always looking for opportunities to reduce network friction where possible.  One example is product change in terms of transport used from BITS to Delivery Optimization (DO) with fallback when downloading files during product installation and update workflow.  Delivery Optimization provides user impersonation which will allow connectivity to internet when an interactive user is logged on with WinINET internet access even if System account has no internet access.  By default, Delivery Optimization as a technology was designed to download portions of the content from peers in their network.  Customers who have investments in SCCM can enable Microsoft Connected Cache in Configuration Manager which can be a powerful combination of these technologies.  In this way, Office can leverage Windows network stack feature Delivery Optimization and combine that with Microsoft Endpoint Configuration Manager for increased network efficiency.  Customers can use Delivery Optimization in Update Compliance dashboard to see metrics about Office peer sharing efficiency.  SCCM IT Pros can reduce operational costs by eliminating need to manually download and distribute static content to Distribution Points and allow Office to dynamically populate cache based on their needs regardless of channel or version and at the same time remain in control of what versions of Office are deployed to their clients.  The transport change to Delivery Optimization for Office downloads is currently rolling out now and should be completed by July 2020 in Semi-Annual Channel.  IT Pros don't need to do anything intentional to take advantage of these enhancements.


Many customers we visit in the field prohibit computers from accessing the internet directly.  Typically, only Users can access the internet through a proxy server or via PAC file.  These User settings are defined as WinINET proxy setting you’ll find in Internet Explorer. 

Standard proxy configuration in Internet ExplorerStandard proxy configuration in Internet Explorer

So, what about the local SYSTEM account needed by SCCM?  If customers allow users and computers access to Office 365 endpoints, everything “just works”.  However, often we find customers only configure network proxy for Users and therefore the “lean install” or update scenarios driven by Office Automatic Updates 2.0 scheduled task may fail when user is not interactively logged on as user impersonation is not possible. (Example: Installation will hang as Office Deployment Tool running as System process will fail when attempting to access Office CDN)


OK, what can we do to solve problem?  Configure network perimeter device to white list Office CDN\URLs or configure additional proxy settings within Windows.



  1. Configure WinHTTP proxy (if no interactive user) as DO runs as Network Service
  2. If DO fails, attempt to fallback to BITS will respect WinINET for System account

*Installs and Updates can still succeed without System proxy via User Impersonation (leverages DO transport to provide feature) through interactive logged on user session who does have internet access but this can limit ability to perform deployments after hours when no user session is present or ensuring update compliance if computers are not logged on regularly.


In my lab I use PSEXEC.EXE to accelerate testing.In my lab I use PSEXEC.EXE to accelerate testing.

From elevated command prompt, run PSEXEC.EXE -s -i cmd.exe.  This will launch cmd.exe process in the SYSTEM context to simulate SCCM package etc.  Type whoami from command line to verify.

nt authority\system

Sample commands to set WinINET and import into WinHTTP:

C:\Windows\System32>bitsadmin /util /setieproxy localsystem MANUAL_PROXY ";*"
C:\Windows\System32>netsh.exe winhttp import proxy source=ie

Sample commands to reset:

C:\windows\system32>bitsadmin /util /setieproxy localsystem RESET
C:\windows\system32>netsh winhttp reset proxy

The proxy server\network team should only allow computer access to internet URLs as defined by Office 365 URLs and IP address ranges document as well as any other URLs that they want to explicitly allow the Computer account to access.  A number of network appliance vendors provide seamless Office 365 integration as a feature by calling Microsoft Graph API to dynamically populate network access list.


In summary, using a “lean” Office 365 ProPlus deployment strategy will greatly reduce complexity and cost of ownership to operate Office 365 ProPlus. 


Additional Reference Documentation and tools for proxy configuration for Windows

Office 365 Network Onboarding tool

Use Group Policy to apply WinHTTP proxy settings to Windows clients

bitsadmin util and setieproxy

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