Digital postal mail startup Zumbox has informed users that it will shut down operations next week.

The Inglewood company, which had raised more than $28 million from venture investors since its founding in 2006, created an email inbox for each home in the markets it served, based on residential street address. Zumbox users would receive digital copies of mail from companies that use the Zumbox system. Home customers then had the option to turn off their paper mail from those companies and receive their correspondence digitally.

But the company faced a number of challenges in getting its business profitable. It also was weakened by legal challenges, such as a 2009 lawsuit by Pitney Bowes Inc. that alleged Zumbox’s “paperless mail” service infringed on its patents.

A Zumbox email to users suggested they export their digital files to another location by Monday. “We are sad to announce … that after more than five years of working to revolutionize the way mail is delivered, we have made the very difficult decision to shut down the company,” said the notice, which first was reported by Matt Swain of the InfoTrends blog. “At this point, the time and cost required to deliver on the vision is more than the market is prepared to invest.”

Zumbox’s backers included Compushare, Shelter Capital Partners and former Walt Disney Co. chief executive Michael Eisner’s investment firm.