U.S. Citizenship and Immigration Services (USCIS) announced on April 20, 2016 that that for two weeks after premium processing resumes for H-1B cap-subject petitions (scheduled to start on May 12, 2016), USCIS will temporarily suspend use of Pre-Paid Mailers. This means that USCIS will not use any provided pre-paid mailers submitted with H-1B cap petitions to return the final notices for premium processing subject H-1B cap petitions. USCIS will instead use regular postal mail.
USCIS has stated that they have instituted this procedure due to resource limitations as they work to process all premium processing petitions in a timely manner. After the two week period, USCIS will resume sending out final notices in pre-paid mailers, if provided by petitioners.