We have been getting a few questions from Customers and Partners about BPOS. One of the questions is "Will BPOS support Outlook 2003?".
It is expected that from June 2009, Outlook 2003 will be supported, but there are clear limitations. See this extract from a MS Field Blog:
Outlook 2003 WILL BE supported in Exchange Online Standard by June 2009. However, there are two very critical caveats:
No Free-Busy: While Exchange Online Standard will support Outlook 2003, the Free-Busy functionality in Outlook 2003 will be completely disabled when connected to Exchange Online. In other words, there will be NO Free-Busy support or capability in Outlook 2003 when used with Exchange Online. We are investigating possible mitigations for this issue, but we cannot commit a date for Free-Busy support in Outlook 2003 when used with Exchange Online.
Possible Workaround: Free-Busy WILL work in OWA. So an end-user could switch to OWA to schedule a meeting when they need to see Free-Busy info for another Online user (note that Exchange Online still will NOT expose Free-Busy information in a co-existence scenario to on-premises users -- this limitation still exists and will not be fixed until Wave 14 - see F/B Coexist Topic)
Outlook 2003 Not Supported By Exchange Online 2010 Version (Wave 14): Be aware that Outlook 2003 support for Exchange Online will end at Wave 14 when Exchange Online moves onto Exchange Server 2010.
Possible Mitigation: Customers have 12 months to opt into platform upgrade of BPOS. So a customer who is on BPOS Standard who needs Outlook 2003 support could have it for up to 12 months after Wave 14 platform upgrade if customer chooses to stay on the current platform. But it does mean they will not get the benefits of Wave 14 capabilities. So customer will have to weigh Outlook 2003 support against Wave 14 benefits.
We will provide more information about exactly what this support will look like shortly. (I.e. will the Sign-In Tool configure Outlook 2003 as it does Outlook 2007, etc.)
Refer to Outlook 2003 WIKI Topic page for subsequent updates.
UPDATE: A third caveat to consider - just added this to the WIKI topic: Outlook 2003 Mainstream Support Ended 4/14/2009: Be aware that mainstream support ended for Outlook 2003 on 4/14/2009. So Outlook 2003 is now in Extended Support phase. Customers currently running Outlook 2003 should be reminded of this when considering to stay with Outlook 2003 versus moving to Office 2007.
Original post from Schweizer IT Professional und TechNet Blog by Stefan Hagenbuch.