When Outlook 2003 is used as an e-mail client on Microsoft Exchange® Server 2003-based systems, the negative impact of transient issues such as high latency, loss of connectivity, and limited bandwidth are significantly reduced.

The key technologies that combine to provide a superior client experience in Outlook 2003 include:

Cached Exchange Mode: significantly makes offline usage seamless and greatly improves experience over low bandwidth connections

MAPI Compression

Network adapter speed awareness

Improved synchronization efficiency and robustness

Automatic conflict resolution

Remote procedure calls (RPC) over HTTP (enables direct Outlook to Exchange Server connection over the Internet)

Enhancements to personal folder (PST) and offline folder (OST) files

The following table lists the back end Exchange server needed for each Outlook 2003 enhancements. 

 

Outlook 2003 Feature

Exchange 5.5

Exchange 2000

Exchange 2003

Cached Exchange Mode

X

X

X

RPC/HTTP

   

X

Smart change synchronization

X

X

X

ICS check-pointing

   

X

Skip Bad Items

   

X

Pre-synchronization reporting

   

X

MAPI compression

   

X

Buffer packing

   

X

Automatic conflict resolution

X

X

X

PST/OST enhancements

 

X

X

Send/Receive Groups improvements

   

X

Switching gears, here are some key benefits only Exchange 2003 can offer:

                1. Improved cluster support

2. Restore Storage Group (allows you to restore databases without the need of a recovery server)

3. Mailbox Recovery Center

4. Support for Volume Shadow Copy service

5. IPSec support between FE and BE servers

6. Cross-forest Kerberos authentication with Outlook 2003

7. FE-BE Kerberos authentication

8. Intelligent Message Filter and other security/filtering features

9. Reduced network traffic due to improved MAPI compression

10. MAPI over HTTPS support

11. Better queue management

12. Improved migration tools

13. Improved administration tools

More Information:

The most important thing to keep in mind is that the vast improvements in Outlook 2003, especially concerning bandwidth utilisation, are only realized when used with Exchange 2003. 

As an example, here's an excellent paper that compares various Outlook clients hitting Exchange 2003 servers (http://www.microsoft.com/exchange/techinfo/outlook/clinettraf.asp).  If you look at the bandwidth usage results starting on page 317, you can see that on an Exchange 2003 server, Outlook 2000 uses 120-180% more bandwidth than Outlook 2003 in cached mode.

http://www.microsoft.com/exchange/techinfo/outlook/clinettraf.asp 

Key Resources:

Enabling a Superior Client Experience with Outlook 2003

http://www.microsoft.com/office/outlook/prodinfo/enabling.mspx

Top 10 Reasons to Upgrade to E2k3:

http://www.microsoft.com/exchange/evaluation/topten.asp

Better Together: Outlook 2003 and Exchange 2003:

http://www.microsoft.com/exchange/evaluation/bettertogether/BT_outlook2003.asp

Comparison chart for Exchange 5.5, 2000, 2003:

http://www.microsoft.com/exchange/evaluation/features/ex_compare.asp

Additional Resources:

Exchange 5.5 to Exchange 2003 Cost Savings Scenarios:

http://www.microsoft.com/exchange/evaluation/ExchangeScenarios.asp

Guide to make a decision between E2k vs E2k3:

http://www.microsoft.com/exchange/evaluation/WhichVersion.asp

E2k3 ROI calculation tools:

http://www.microsoft.com/exchange/evaluation/roi/default.asp:

E2k3 TCO document:

http://www.microsoft.com/exchange/evaluation/TotalCost.asp

E2k3 Business Value:

http://www.microsoft.com/exchange/evaluation/roi/BizValueE2k3.asp

Cost of Migrating to Exchange 2003:

http://www.microsoft.com/exchange/evaluation/MigrateLowCost.asp