The $US9.99 Mac version featured POP and IMAP support, integration with DropBox and CloudApp for 'sending' large attachments as links.
Other features included a collapsable interface, quick reply (for situations where a message only needs a brief response), and Facebook Connect support.
The user interface of the $2.99 iOS version made use of swiping for multiple functions including switching between mailboxes, uncovering folders, and labelling messages.
Sparrow will remain on the market and customers will be supported, but no significant development will occur.
Financial terms of the acquisition were not disclosed, but citing "sources close to the acquisition," The Verge reports the price was under $25 million.