Only the "letter" and "flat" options require the additional cost for certification.
The USPS does not allow Delivery Confirmation for packages/thick envelopes less than 3/4" thick. If you want to ship a 1oz package or thick envelope via First Class Mail, you must select the "Package" option from the drop-down menu, and you will only be charged the postage fee plus the .19 surcharge for Delivery Confirmation.
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