As stated above, with the Desktop version you get 5 free Federal e-files (the limit of 5 federal e-files is restricted by the IRS). Any returns after the 5 Federal e-files would have to be mailed in.
For Tax preparers and to do more than 5 e-files, you would need the following software
TurboTax ProSeries:
http://proseries.intuit.com/products/
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The IRS requires you to have an Preparer Tax Identification Number (PTIN) which designates you as a professional preparer. To get one, you need to register through the IRS.
http://www.irs.gov/Tax-Professionals/PTIN-Requirements-for-Tax-Return-Preparers
