Apple has rejected an update to Sparrow for iPhone, and the app will be removed from the App Store unless it can submit a new version, says developer Dinh Viet Hoa. The team plans to submit a new version of the app that is compatible with iOS 6 only.

“We managed to get a rich text edition [and] the keyboard appeared without the user [having] to tap on iOS 5,” says Viet Hoa, about the reasons for the rejection. The way those tweaks were implemented apparently violated enough rules for Apple to reject the app. Rich text editing in email was a feature Apple added in iOS 6, it was not available in iOS 5.

This is despite the app being relegated to ‘bug fix only’ status after the team was acquired back in July by Google, to work on its email clients.

There have actually been several updates to the app since its acquisition, including support for Google’s new ‘Open in Chrome’ actions, which it has been bringing to all of its official apps. A recent update to Sparrow for Mac brought support for Apple’s Retina display and Mountain Lion’s Notification Center.

Google acquired the Sparrow team for its Gmail efforts, with Leca stating that they were “joining the Gmail team to accomplish a bigger vision — one that we think we can better achieve with Google.”

At that time, Leca said that they did not plan to release any new features for the Sparrow apps, and likely no iPad version either. Yet, the app has seen the update above to add at least one Google-friendly feature, and iPhone 5 support is certainly welcome.

For more on Sparrow, you can check out our interview with company founder Dom Leca here.