Spark Review

• Sends statistical data to several services known for bad privacy policies (Google, Facebook), also there's no way to opt out.
• Automatically creates an acount with the first address entered and subscribes you to their newsletter.
• Stores credentials for your email accounts on their servers.
• Stores your emails on their servers to push them to your devices.
• Server infrastructure seems to be located in the US.

Many services such as Spam filters, Pocket, and other apps are not supported.

• On the Mac platform will show +999 for the folder that contains more than 1000 emails.
• On the iPhone, the platform will not show the counts next to the folder unless they are new emails.