In 2006, Congress passed the Pension Protection Act. And it included an idea that seemed simple at the time. The idea was that the IRS should know how many tax-exempt organizations existed in the country. The result (part of the Pension Act) is known as the 990 e-Postcard Notification Law, which became effective this past July. It was aimed at all those small (sometimes very small) organizations that generate less than $5,000 each year, never have had to file for tax-exempt status and don't have to file a Form 990 annually.
To keep it simple, the law said the e-Postcard had to be filed online. In fact, there is no other way to make the filing. There is no paper equivalent of the e-Postcard--everything about it is supposed to be electronic, including the IRS's replies.