According to the IRS instructions for Form 8879:
Form 8879 - Retention Requirements
IRS e-file processing sites have received Forms 8879, IRS e-file Signature Authorization, submitted in error. Form 8879 instructions and Publication 1345 require Electronic Return Originators to retain the completed Form 8879 for 3 years from the return due date, or IRS received date, whichever is later.
The retention requirements above also apply to Form 8878, IRS e-file Signature Authorization - Application for Extension of Time to File.
This information applies to all years of the UltimateTax software.