A tool that allows Microsoft Outlook users to migrate over Google's Gmail is at the centre of a patent infringement case.

Start-up firm LimitNone LLC has filed a complaint in an Illinois circuit court alleging that Google at first began promoting the smaller firm's tool for migrating Microsoft Outlook customers to Gmail, then copied the idea and went into competition with it, reports Reuters.

In the case notes, LimitNone states that it started meetings with Google in March 2007 negotiating about building a tool it called "gMove".

This was designed specifically for moving the email, address books and calendars of corporate customers from Microsoft Outlook into Gmail.

LimitNone alleges that Google was having trouble building a similar tool.

The start-up claims it then entered into a confidentiality deal with Google "to share trade secrets of its e-mail migration tool with Google engineers, sales people and key Google Apps customers".

But last December, the company, which has five employees, says that it found that that Google planned to market its tool by itself.

Lead plaintiff's attorney David Rammelt said in a phone interview with Reuters that LimitNone was 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 $950 million".

LimitNone is seeking "reimbursement from Google of actual damages, attorneys' fees and calls on the court to award punitive damages".

Google is not commenitng on the case.