The retention rule
Form 8879 instructs the ERO to retain the completed form for 3 years from the return due date or IRS received date, whichever is later, and not to send it to the IRS unless requested.
The IRS e-signature FAQ adds that an e-signed record must be kept tamper-proof in a secure, access-controlled storage system for 3 years from the due date of the return or from the IRS receipt date, whichever is later.

