Google has been accused of copying email migration software from another company to create Google Email Uploader.
LimitNone has filed a lawsuit against Google, claiming that it shared details of its email migration tool in a bid to help Google build 'gMove' - a similar tool for moving the email, address books and calendars of corporate customers from Microsoft Outlook into Gmail.
LimitNone claims Google then copied the idea and built it into Google Email Uploader. The lawsuit alleges that Google Email Uploader is "almost identical" to gMove and that "both operate under a similar conceptual design".
LimitNone is seeking reimbursement from Google of actual damages, attorneys' fees and also punitive damages.
LimitNone's attorney David Rammelt told Reuters that the company had been told by Google that 50 million subscribers was "just too big to come from someone else" and that a simple calculation of the lost revenue for LimitNone "very quickly gets you up to about $950m (£475m)".
Google was not available to comment at the time of writing.