Many customers have asked us to support Outlook 2003 in order to help accelerate their migrations to Office 365.  We have heard these requests loud and clear. 

In an effort to better facilitate the transition for our customers, we will now offer support for Office 365 customers connecting to Outlook 2003 via POP or IMAP.  Outlook 2003 will only connect to Exchange Online via POP or IMAP, as MAPI-based connection is not possible with this client version and a cloud service. 
Using Outlook 2003 with POP or IMAP enables standard email functionality, but does have key limitations including:

• No calendar information
• No free/busy information
• No Global Address List
• No push email
• When connecting via POP, all messages will be downloaded to the client and there will be no synchronization between multiple computers or devices (such as between a laptop and a phone)

While we strongly recommend that Office 365 customers use Office 2010 to ensure the best user experience and support, we hope this new support for Outlook 2003 helps make the move to Office 365 even faster and easier.

See also

• "Office 2003 - unsupported with Office 365. But will it work?" - link