Have You Considered?

When working with Exchange, there are some factors that you may need to consider to get the most out of the product. Here are some aspects that may help you…

Online Mode

  • Better for mailboxes over 2GB mailbox size (this is due to the desktop client system resource limitations – CPU, Memory, Disk speed, etc)
  • Secure in that all messages are stored on the server and no content is downloaded to the client
  • Mail delivery on the client and viewing of new users in the GAL is instant (no polling or OAB download required)
  • Requires active connection to the server to work. So any service (server) disruptions are felt by Online Clients
  • Cost of the backend mailbox server resources grows when clients are in Online mode (Memory, CPU, Disk IO, etc)
  • Outlook Views limitations apply (if users have more than 5,000 objects in a folder, performance delays occur!!)
  • All work is done on the server (not good)
  • In most cases, Online Client performance is significantly worse than cached mode clients
  • Search is restricted to online client search (all work done on the server)
  • Greater chance of one client impacting the server performance and all other connected client’s

Cached Mode

  • Best option for remote clients and/or mailboxes under 2GB in size
  • Allows users to work offline. Cached mode clients can still function during service (server) disruptions
  • Much better solution for Disaster Recovery scenarios
  • Able to use EFS to secure local cached files (OST and OAB) on desktops
  • Reduce server-side disk IO
  • Outlook views limitations does not apply
  • Reduced chance of 1 client impacting the overall server’s performance
  • Improved Search on the client!!
  • Most work is done on the client – thus releasing server side resources
  • Recommended configuration by most vendors that interact with Outlook or Exchange
  • Not the best solution for mailboxes over 2GB (see online mode comments)
  • Users have to grow accustomed to how mail is downloaded in Cached Mode (easy work around for this!). This sometimes causes a perception that Blackberry receives the mail faster than Outlook.
  • New Users are not shown in the GAL until the client downloads the Offline Address Book (default is every 24hours – can be changed via GPO)

RPC over TCP

  • Direct Connection to Mailbox Server by Client which can impact Mailbox Server performance
  • Clients cannot connect from the Internet without a VPN solution, unless firewall ports are opened (NOT RECOMMENDED!)
  • Less Secure communications than HTTPS
  • Cost to support and manage RPC OVER TCP is usually higher (i.e. network design, backend mailbox server configuration, managing client connections, security, etc)

RPC Over HTTPS (Outlook Anywhere)

  • Connects through Client Access Server (CAS) to obtain mailbox data. This reduces performance impact on the Mailbox Server by offloading conversion to the CAS
  • Most hardware network accelerators work with RPC OVER HTTPS to improve performance
  • More secure method of client to server communication based on SSL Certificate
  • Easier to lock down port security between server and client subnets
  • Clients can connect over the Internet without a VPN connection
  • Works well with ISA and IAG for additional security outside of the organization with requiring VPN
  • Requires SSL for Server and Client communication

Windows XP

  • Users are familiar with OS
  • Most limitations are well known by now because of product maturity
  • Almost all client hardware works well with this OS
  • Product Lifecycle is ½ through support

Windows Vista

  • A more secure and stable platform than XP
  • Improved performance and reliability (i.e. SMB, Self-Healing NTFS, etc)
  • New client features
  • Product is still well within its Product Support Lifecycle
  • Most Hardware vendors have appropriate drivers readily available for Vista
  • Improved server to client communication performance
  • Typically requires some end-user and administrator education on the changes of the OS

Windows 7

  • Same as Vista but includes a more secure, stable platform with improved performance and security than previous versions of Windows
  • Offers new features (when used with Windows Server 2008 R2) such as DirectAccess, and BranchCache
  • Able to secure the applications and computer using Bitlocker and Applocker
  • Improved client productivity with Windows 7 enterprise search functionality and the Windows Troubleshooting Platform
  • Product is just entering its Product Support Lifecycle

Windows Mobile (ActiveSync)

  • Security of device and connection is secure
  • Certified for government use
  • Does not require a service account to be able to access all mailboxes
  • Activesync support is included in Microsoft Premier contract – no additional contract required
  • Cost is minimal – device & device service only
  • No performance impact to Exchange – equivalent to OWA user
  • Users are able to manage devices in OWA or desktop
  • Use of ActiveSync & Device policies to manage services
  • High availability of Activesync is available based on Exchange HA design – no additional requirements


  • Security of device and connection is secure
  • Certified for government use
  • Requires service account access to all mailboxes and root level SQL access
  • Higher cost – device, device service, Blackberry license, BES support
  • Requires additional servers to be installed in environment (SQL & BES)
  • Impact on Exchange is severe (4x IO)
  • Users are familiar with device and technology
  • High Availability is limited - requires 3rd party solution for site resiliency
  • User can manage devices from desktop

There are many other factors involved but hopefully this provides some insight.


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