Well, I suppose you could actually put the PST file up on dropbox, but accessing it the way you normally would in Outlook would not be possible, unless dropbox provides you a path to access it (which from my research they do not allow) What you may want to do is get an email account that allows for IMAP support. Using IMAP may allow you to put the folders outside of a PST and then use something like mobile me to sync all your systems. But to the question of the cloud based solution and just putting your PST up on Dropbox, you could do this, but you would not be able to access it the way you are looking to access it. I hope this helps answer your question, even though it may not be the one you were looking for. If this has answered your question, please click the ACCEPT button on this answer. Positive feedback would be greatly appreciated.