The 5 return efiling limit is set by the IRS. It is part of the Online efiling agreement.
Additional Requirements for Participants in Online Filing In addition to the above, participants in Online Filing must adhere to the following: 1. Ensure that no more than five electronic returns are filed from one software package or one e-mail address. https://www.irs.gov/pub/irs-pdf/p1345.pdf
Per Intuit's guidelines (How many tax returns can I file with TurboTax? ), if you use Turbo Tax Desktop, you can file five federal returns with up to three state returns each. Also no more than five Intuit accounts and five corresponding federal returns (for example, for a family of five) may be created, purchased, and filed using any one email address.
