Exchange Online allows you to move mailboxes from your on-premise Exchange implementation into Exchange Online (and visa-versa), but it doesn't have a feature to import those PST files sitting on your user’s PCs into Exchange Online. Well, not until last week anyway, when Microsoft released a PST import tool which is designed to do just that.

Move your user’s PSTs into Exchange Online or Exchange on-premise with this new tool called “PST Capture”.

Check it out and download it here on the Exchange Server team’s blog