USCIS decided to accept the delayed and rejected applications, provided that the resubmissions include “individualized proof” that the applications were originally mailed in a timely matter and that the delivery delay was because of USPS error.
DHS Secretary did not explain what constitutes "proof of timely filing" (further instructions will be posted on USCIS website soon). Applicants who do not have such documentation can contact USPS to review their cases. Post Office will provide applicants with letters to submit to USCIS with the resubmissions, if appropriate.
USCIS also discovered that it rejected some timely-filed DACA applications in error (applications were received at PO Box address on time), and will reach out to those applicants to advise them to resubmit their applications. Those not contacted by the USCIS who believe their applications were erroneously rejected may also resubmit their applications with proof that their applications were received timely at the designated filing location.