Hello, Is it possible to Install Mailbox,CAS,HUB transport and Unified Communication role on one server ??If yes please do let me know the procedure and if not possible please let me know why.Thanks

Yes, you can install all Exchange roles in a server but you need to do proper sizing with memory, disk and processor to handle the load. Refer below articles to get further information... How to Perform a Custom Installation Using Exchange Server 2007 Setup http://technet.microsoft.com/en-us/library/bb125143.aspx Planning Your Server and Storage Architecture http://technet.microsoft.com/en-us/library/bb738142.aspx Exchange 2007 Sizing Cheat Sheet http://www.msexchange.org/articles-tutorials/exchange-server-2007/planning-architecture/exchange-2007-sizing-cheat-sheet.htmlAmit Tank | MVP Exchange Server | MCITP: EMA | MCSA: M | http://ExchangeShare.WordPress.com