There has been a lot of speculation about the iPhone and its abilities to connect to Microsoft Exchange Server. For instance, Wall Street Journal columnist Walt Mossberg mentions in his June 26 All Things Digital column that, "It [the iPhone] can also handle corporate email using Microsoft's Exchange system, if your IT department cooperates by enabling a setting on the server."
Technically this is correct, as today iPhone users can connect to Microsoft Exchange using IMAP. There are, however, some significant differences in the mobile device experience and IT professional capabilities supported by IMAP on the iPhone and those enabled by Exchange ActiveSync (EAS) for compatible devices. EAS is a protocol that provides rich messaging experiences for over 200 different smartphones right out of the box. These smartphones include Windows Mobile devices as well as phones from a broad range of 3rd parties including Helio, Motorola, Nokia, Palm, Sony Ericsson and others.
Comparing IMAP and EAS at a high level: IMAP provides an adequate mobile email experience (but is subject to some important limitations), whereas EAS provides a more secure, complete companion experience to Outlook and Outlook Web Access (OWA) for the mobile device. To better understand this comparison, let's look at IMAP on the iPhone and EAS in a bit more detail from several perspectives:
The mobile experience beyond email
IMAP enables an adequate mobile email experience; EAS enables the additional pieces that make mobile email great
Both IMAP and EAS give the mobile client the capability to read email with rich html formatting, and view their inbox as well as subfolders of their inbox and reply/reply-all/forward/compose email (technically, the iPhone uses SMTP to send email. SMTP for outbound email is configured along during IMAP/Exchange account setup on the device).
EAS also supports capabilities for:
Direct Push, which provides an up-to-date messaging experience designed for mobile networks
Email flagging to improve the triage experience on the device
AutoDiscover to simplify the process of setting up a new device over-the-air
Server-side logic to preserve the formatting of rich email on reply/forward if the mobile client doesn't support rich html editing (most don't)
Numerous bandwidth optimizations to reduce data charges and improve battery life
EAS enables a rich collaboration experience beyond email
A significant part of the Exchange user experience goes beyond email. The IMAP protocol only supports email. EAS is designed to enable a great over-the-air companion experience to Outlook and OWA and supports many facets of Exchange beyond email, including:
Contact synchronization - view, create and update contacts
Calendar synchronization - view, create & update appointments, schedule meetings, and accept/decline/propose new time for meeting requests
Global Address List (GAL) lookup - look-up users in your corporate directory
Out-of-office (OOF) email responses - turn on/off and change the OOF message directly from your mobile phone
Access to documents stored in Sharepoint document libraries and UNC shares
Search your entire mailbox on the server regardless of what's cached on the mobile phone
Allowing users to manage their mobile device(s) using OWA - see device activity, help retrieve forgotten PIN, remotely wipe lost device, etc
EAS and IMAP both secure data on the network; EAS also protects data once it's on the device
From an IT department's perspective, this is a highly important distinction between IMAP and EAS.
Both IMAP and EAS allow IT to ensure data and credentials are protected on the network by encrypting them via SSL.
Many IT departments require support for additional security measures to protect data on the device as well (not just over the network) to guard against loss or theft before they are willing to let users connect to Exchange from the Internet using a given protocol. Only EAS addresses this requirement by enabling IT to implement and enforce security policies that protect the data once it's on the device. There are a number of these policies supported by EAS today and we continue to add more, some key examples are:
Requiring a PIN lock on the device
IT also has a number of controls dictating the strength of the PIN, timeout, etc. as well as the ability to recover forgotten PINs
Local and Remote Wipe
IT can require that the device erases all data (including data on the SD card) in the event that (1) the PIN is incorrectly entered an IT-specified number of times or (2) IT or the user issues a remote wipe command from the admin console or OWA.
Blocking attachment download to the device
Limiting which Sharepoint libraries / UNC shares the user can access
Because IMAP does not support these security policies, many IT departments have decided not to enable mobile device (or any Internet client) access to email via IMAP. EAS on the other hand is seeing increasingly broad adoption by IT departments.
Microsoft Exchange does have IMAP support that provides for an adequate email experience. The iPhone can access email via IMAP if the IT department has enabled IMAP connectivity for users. However, IMAP has limitations from both an IT and user standpoint with respect to security and richness of experience that prevent it from being a complete solution for mobile device access to Microsoft Exchange.
Exchange ActiveSync on the other hand provides a very rich email and collaboration experience for end-users as well as support for the important security measures needed for IT.