A fronte di una richiesta che mi è pervenuta un paio di mesi fa da un partner, ecco i risultati della mia ricerca:

The following will work fine with WSS running in conjunction with Exchange 5.5:

• The ability to send Alerts, Notifications and E-mails from SharePoint Lists and Libraries.
• The ability to E-mail enable SharePoint Lists and Libraries to receive E-mails.
• Index and crawl Exchange 5.5 Public Folders for users to search. (La procedura risulta piuttosto complicata)

The following are some of the salient features that are only available with Outlook 2007 and Exchange 2007, will not work with Exchange 5.5:

• The ability to take SharePoint Lists data offline in Outlook.
• Directly sending an E-mail for archival to a Wss Records center using Managed folders in Outlook.
• The Link Access feature that allows you to access SharePoint sites and file shares through Outlook Web Access, eliminating the need to expose your internal SharePoint topology or files shares to the Internet or require a virtual private network (VPN) connection to gain access.

Ricordo inoltre che Microsoft Exchange 5.5 non è più supportato.

Informazioni sul ciclo di vita del supporto per categoria di prodotto
http://support.microsoft.com/lifecycle/?p1=1776